Mysql 简明教程
MySQL - Introduction
What is a Database?
数据库是一个存储数据集合的单独应用程序。每个数据库都有一个或多个不同的 API，用于创建、访问、管理、搜索和复制它所保存的数据。
A database is a separate application that stores a collection of data. Each database has one or more distinct APIs for creating, accessing, managing, searching and replicating the data it holds.
还可以使用其他种类的数据存储，例如文件系统上的文件或内存中的大型哈希表，但是使用这些类型的系统进行数据获取和写入不会如此快速和容易。
Other kinds of data stores can also be used, such as files on the file system or large hash tables in memory but data fetching and writing would not be so fast and easy with those type of systems.
如今，我们使用关系数据库管理系统 (RDBMS) 来存储和管理海量数据。这被称为关系数据库，因为所有数据都存储到不同的表中，并且使用主键或称为 Foreign Keys 的其他密钥建立关系。
Nowadays, we use relational database management systems (RDBMS) to store and manage huge volume of data. This is called relational database because all the data is stored into different tables and relations are established using primary keys or other keys known as Foreign Keys.
Relational DataBase Management System (RDBMS) 是一个软件 −
A Relational DataBase Management System (RDBMS) is a software that −
-
Enables you to implement a database with tables, columns and indexes.
-
Guarantees the Referential Integrity between rows of various tables.
-
Updates the indexes automatically.
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Interprets an SQL query and combines information from various tables.
RDBMS Terminology
在我们继续解释 MySQL 数据库系统之前，让我们复习几个与数据库相关的定义。
Before we proceed to explain the MySQL database system, let us revise a few definitions related to the database.
-
Database − A database is a collection of tables, with related data.
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Table − A table is a matrix with data. A table in a database looks like a simple spreadsheet.
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Column − One column (data element) contains data of one and the same kind, for example the column postcode.
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Row − A row (= tuple, entry or record) is a group of related data, for example the data of one subscription.
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Redundancy − Storing data twice, redundantly to make the system faster.
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Primary Key − A primary key is unique. A key value can not occur twice in one table. With a key, you can only find one row.
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Foreign Key − A foreign key is the linking pin between two tables.
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Compound Key − A compound key (composite key) is a key that consists of multiple columns, because one column is not sufficiently unique.
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Index − An index in a database resembles an index at the back of a book.
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Referential Integrity − Referential Integrity makes sure that a foreign key value always points to an existing row.
MySQL Database
MySQL 是一个快速、易于使用的 RDBMS，被许多中小型企业使用。MySQL 由瑞典公司 MySQL AB 开发、销售和支持。MySQL 变得如此流行有很多原因-
MySQL is a fast, easy-to-use RDBMS being used for many small and big businesses. MySQL is developed, marketed and supported by MySQL AB, which is a Swedish company. MySQL is becoming so popular because of many good reasons −
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MySQL is released under an open-source license. So you have nothing to pay to use it.
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MySQL is a very powerful program in its own right. It handles a large subset of the functionality of the most expensive and powerful database packages.
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MySQL uses a standard form of the well-known SQL data language.
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MySQL works on many operating systems and with many languages including PHP, PERL, C, C++, JAVA, etc.
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MySQL works very quickly and works well even with large data sets.
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MySQL is very friendly to PHP, the most appreciated language for web development.
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MySQL supports large databases, up to 50 million rows or more in a table. The default file size limit for a table is 4GB, but you can increase this (if your operating system can handle it) to a theoretical limit of 8 million terabytes (TB).
-
MySQL is customizable. The open-source GPL license allows programmers to modify the MySQL software to fit their own specific environments.
Before You Begin
在开始本教程之前，您应该对我们 PHP 和 HTML 教程中涵盖的信息有基本的了解。
Before you begin this tutorial, you should have a basic knowledge of the information covered in our PHP and HTML tutorials.
本教程重点介绍在 PHP 环境中使用 MySQL。本教程给出的许多示例对 PHP 程序员来说很有用。
This tutorial focuses heavily on using MySQL in a PHP environment. Many examples given in this tutorial will be useful for PHP Programmers.
我们建议您查看我们的 PHP Tutorial 以供参考。
We recommend you check our PHP Tutorial for your reference.
MySQL - Installation
MySQL 的所有下载都位于 MySQL Downloads 。选择所需的 MySQL Community Server 版本号以及您将运行它的平台。
All downloads for MySQL are located at MySQL Downloads. Pick the version number of MySQL Community Server which is required along with the platform you will be running it on.
Installing MySQL on Linux/UNIX
在 Linux 系统上安装 MySQL 的推荐方法是通过 RPM。MySQL AB 使以下 RPM 可在其网站上下载 −
The recommended way to install MySQL on a Linux system is via RPM. MySQL AB makes the following RPMs available for download on its website −
-
MySQL − The MySQL database server manages the databases and tables, controls user access and processes the SQL queries.
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MySQL-client − MySQL client programs, which make it possible to connect to and interact with the server.
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MySQL-devel − Libraries and header files that come in handy when compiling other programs that use MySQL.
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MySQL-shared − Shared libraries for the MySQL client.
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MySQL-bench − Benchmark and performance testing tools for the MySQL database server.
此处列出的 MySQL RPM 都是基于一个 SuSE Linux system 构建的，但它们通常可以在其他 Linux 变体上工作，没有困难。
The MySQL RPMs listed here are all built on a SuSE Linux system, but they will usually work on other Linux variants with no difficulty.
现在，你需要遵守以下步骤，以继续安装 −
Now, you will need to adhere to the steps given below, to proceed with the installation −
-
Login to the system using the root user.
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Switch to the directory containing the RPMs.
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Install the MySQL database server by executing the following command. Remember to replace the filename in italics with the file name of your RPM.
[root@host]# rpm -i MySQL-5.0.9-0.i386.rpm上述命令负责安装 MySQL 服务器、创建 MySQL 用户、创建必要的配置并自动启动 MySQL 服务器。
The above command takes care of installing the MySQL server, creating a user of MySQL, creating necessary configuration and starting the MySQL server automatically.
你可以在 /usr/bin 和 /usr/sbin 中找到所有与 MySQL 相关的二进制文件。所有表和数据库都将创建在 /var/lib/mysql 目录中。
You can find all the MySQL related binaries in /usr/bin and /usr/sbin. All the tables and databases will be created in the /var/lib/mysql directory.
以下代码框有一个可选但推荐的步骤，以相同的方式安装其余的 RPM −
The following code box has an optional but recommended step to install the remaining RPMs in the same manner −
[root@host]# rpm -i MySQL-client-5.0.9-0.i386.rpm
[root@host]# rpm -i MySQL-devel-5.0.9-0.i386.rpm
[root@host]# rpm -i MySQL-shared-5.0.9-0.i386.rpm
[root@host]# rpm -i MySQL-bench-5.0.9-0.i386.rpmInstalling MySQL on Windows
现在，任何版本的 Windows 上的默认安装都比以前容易得多，因为 MySQL 现在与安装程序整齐地打包在一起。只需下载安装程序包，将其解压缩到任意位置并运行 setup.exe 文件即可。
The default installation on any version of Windows is now much easier than it used to be, as MySQL now comes neatly packaged with an installer. Simply download the installer package, unzip it anywhere and run the setup.exe file.
默认安装程序 setup.exe 将带你浏览简单流程，并且默认将一切安装在 C:\mysql 下。
The default installer setup.exe will walk you through the trivial process and by default will install everything under C:\mysql.
首次通过命令提示符启动它来测试服务器。转到 mysqld server 的位置，它可能为 C:\mysql\bin，然后键入 −
Test the server by firing it up from the command prompt the first time. Go to the location of the mysqld server which is probably C:\mysql\bin, and type −
mysqld.exe --consoleNOTE − 如果在 NT 上，则必须使用 mysqld-nt.exe 而不是 mysqld.exe
NOTE − If you are on NT, then you will have to use mysqld-nt.exe instead of mysqld.exe
如果一切顺利，你将看到一些关于启动和 InnoDB 的消息。如果不是这样，你可能有权限问题。确保保存数据的目录可供任何用户（可能是 MySQL）访问，这些用户在数据库进程运行期间运行。
If all went well, you will see some messages about startup and InnoDB. If not, you may have a permissions issue. Make sure that the directory that holds your data is accessible to whatever user (probably MySQL) the database processes run under.
MySQL 不会将自身添加到开始菜单中，并且也没有特别好的 GUI 方式来停止服务器。因此，如果你倾向于通过双击 mysqld 可执行文件来启动服务器，你应记住通过使用 mysqladmin、任务列表、任务管理器或其他 Windows 特定方式手动停止进程。
MySQL will not add itself to the start menu, and there is no particularly nice GUI way to stop the server either. Therefore, if you tend to start the server by double clicking the mysqld executable, you should remember to halt the process by hand by using mysqladmin, Task List, Task Manager, or other Windows-specific means.
Verifying MySQL Installation
MySQL 安装成功后，基本表格已初始化，并且服务器已启动：你可以通过一些简单测试来验证一切是否按预期工作。
After MySQL, has been successfully installed, the base tables have been initialized and the server has been started: you can verify that everything is working as it should be via some simple tests.
Use the mysqladmin Utility to Obtain Server Status
使用 mysqladmin 二进制检查服务器版本。该二进制文件在 Linux 上的 /usr/bin 中可用，在 Windows 上的 C:\mysql\bin 中可用。
Use mysqladmin binary to check the server version. This binary would be available in /usr/bin on linux and in C:\mysql\bin on windows.
[root@host]# mysqladmin --version它将在 Linux 上生成以下结果。它可能随你的安装而变化 −
It will produce the following result on Linux. It may vary depending on your installation −
mysqladmin Ver 8.23 Distrib 5.0.9-0, for redhat-linux-gnu on i386如果你没有收到这样的消息，那么你的安装中可能存在一些问题，你需要一些帮助来解决它。
If you do not get such a message, then there may be some problem in your installation and you would need some help to fix it.
Execute simple SQL commands using the MySQL Client
你可以通过 MySQL 客户端和使用 mysql 命令连接到你的 MySQL 服务器。此时，你不需要提供任何密码，因为它默认设置为空白。
You can connect to your MySQL server through the MySQL client and by using the mysql command. At this moment, you do not need to give any password as by default it will be set as blank.
你可以仅使用以下命令 −
You can just use following command −
[root@host]# mysql它应带有 mysql> 提示。现在，你已连接到 MySQL 服务器，你可以按照以下步骤在 mysql> 提示符下执行所有 SQL 命令 −
It should be rewarded with a mysql> prompt. Now, you are connected to the MySQL server and you can execute all the SQL commands at the mysql> prompt as follows −
mysql> SHOW DATABASES;
+----------+
| Database |
+----------+
| mysql |
| test |
+----------+
2 rows in set (0.13 sec)Post-installation Steps
MySQL 为 root MySQL 用户提供空白密码。只要你成功安装数据库和客户端，就需要按照以下代码块中所述设置 root 密码 −
MySQL ships with a blank password for the root MySQL user. As soon as you have successfully installed the database and the client, you need to set a root password as given in the following code block −
[root@host]# mysqladmin -u root password "new_password";现在要连接到你的 MySQL 服务器，你必须使用以下命令 −
Now to make a connection to your MySQL server, you would have to use the following command −
[root@host]# mysql -u root -p
Enter password:*******UNIX 用户还希望在 PATH 中放置你的 MySQL 目录，这样你就不必在每次要使用命令行客户端时都键入完整路径。
UNIX users will also want to put your MySQL directory in your PATH, so you won’t have to keep typing out the full path everytime you want to use the command-line client.
对于 bash，它类似于以下内容 −
For bash, it would be something like −
export PATH = $PATH:/usr/bin:/usr/sbinRunning MySQL at Boot Time
如果你要在引导时运行 MySQL 服务器，则确保在 /etc/rc.local 文件中有以下条目。
If you want to run the MySQL server at boot time, then make sure you have the following entry in the /etc/rc.local file.
/etc/init.d/mysqld start此外，你应在 /etc/init.d/ 目录中包含 mysqld 二进制文件。
Also,you should have the mysqld binary in the /etc/init.d/ directory.
MySQL - Administration
Running and Shutting down MySQL Server
首先检查你的 MySQL 服务器是否正在运行。你可以使用以下命令检查它 −
First check if your MySQL server is running or not. You can use the following command to check it −
ps -ef | grep mysqld如果您的 MySQL 正在运行，那么您将在结果中看到 mysqld 进程。如果服务器没有运行，那么您可以使用以下命令启动服务器：
If your MySql is running, then you will see mysqld process listed out in your result. If server is not running, then you can start it by using the following command −
root@host# cd /usr/bin
./safe_mysqld &现在，如果您想关闭已经运行的 MySQL 服务器，那么您可以使用以下命令执行此操作：
Now, if you want to shut down an already running MySQL server, then you can do it by using the following command −
root@host# cd /usr/bin
./mysqladmin -u root -p shutdown
Enter password: ******Setting Up a MySQL User Account
若要向 MySQL 添加新用户，您只需在数据库 mysql 中的 user 表中添加一个新条目。
For adding a new user to MySQL, you just need to add a new entry to the user table in the database mysql.
以下程序是使用密码 guest123; 为新用户 guest 添加 SELECT、INSERT 和 UPDATE 权限的示例，SQL 查询如下：
The following program is an example of adding a new user guest with SELECT, INSERT and UPDATE privileges with the password guest123; the SQL query is −
root@host# mysql -u root -p
Enter password:*******
mysql> use mysql;
Database changed
mysql> INSERT INTO user
(host, user, password,
select_priv, insert_priv, update_priv)
VALUES ('localhost', 'guest',
PASSWORD('guest123'), 'Y', 'Y', 'Y');
Query OK, 1 row affected (0.20 sec)
mysql> FLUSH PRIVILEGES;
Query OK, 1 row affected (0.01 sec)
mysql> SELECT host, user, password FROM user WHERE user = 'guest';
+-----------+---------+------------------+
| host | user | password |
+-----------+---------+------------------+
| localhost | guest | 6f8c114b58f2ce9e |
+-----------+---------+------------------+
1 row in set (0.00 sec)添加新用户时，请记住使用 MySQL 提供的 PASSWORD() 函数对新密码进行加密。正如您在上面的示例中看到的，密码 mypass 被加密为 6f8c114b58f2ce9e。
When adding a new user, remember to encrypt the new password using PASSWORD() function provided by MySQL. As you can see in the above example, the password mypass is encrypted to 6f8c114b58f2ce9e.
注意 FLUSH PRIVILEGES 语句。这会告诉服务器重新加载授予表。如果您不使用它，那么至少在服务器重新启动之前，您将无法使用新用户帐户连接到 MySQL。
Notice the FLUSH PRIVILEGES statement. This tells the server to reload the grant tables. If you don’t use it, then you won’t be able to connect to MySQL using the new user account at least until the server is rebooted.
您还可以通过在执行 INSERT 查询时将用户表中以下列的值设置为“Y”来为新用户指定其他权限，或者稍后使用 UPDATE 查询更新它们。
You can also specify other privileges to a new user by setting the values of following columns in user table to 'Y' when executing the INSERT query or you can update them later using UPDATE query.
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Select_priv
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Insert_priv
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Update_priv
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Delete_priv
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Create_priv
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Drop_priv
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Reload_priv
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Shutdown_priv
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Process_priv
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File_priv
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Grant_priv
-
References_priv
-
Index_priv
-
Alter_priv
添加用户帐户的另一种方法是使用 GRANT SQL 命令。以下示例将为名为 TUTORIALS 的特定数据库添加带有密码 zara123 的用户 zara 。
Another way of adding user account is by using GRANT SQL command. The following example will add user zara with password zara123 for a particular database, which is named as TUTORIALS.
root@host# mysql -u root -p password;
Enter password:*******
mysql> use mysql;
Database changed
mysql> GRANT SELECT,INSERT,UPDATE,DELETE,CREATE,DROP
-> ON TUTORIALS.*
-> TO 'zara'@'localhost'
-> IDENTIFIED BY 'zara123';这还将在名为 user 的 MySQL 数据库表中创建一个条目。
This will also create an entry in the MySQL database table called as user.
NOTE − 在 SQL 命令的末尾加上分号 (;) 之前，MySQL 不会终止一个命令。
NOTE − MySQL does not terminate a command until you give a semi colon (;) at the end of the SQL command.
The /etc/my.cnf File Configuration
在大部分情况下，您不应该触碰此文件。默认情况下，它将具有以下条目：
In most of the cases, you should not touch this file. By default, it will have the following entries −
[mysqld]
datadir = /var/lib/mysql
socket = /var/lib/mysql/mysql.sock
[mysql.server]
user = mysql
basedir = /var/lib
[safe_mysqld]
err-log = /var/log/mysqld.log
pid-file = /var/run/mysqld/mysqld.pid在这里，您可以为错误日志指定一个不同的目录，否则您不应该更改此表中的任何条目。
Here, you can specify a different directory for the error log, otherwise you should not change any entry in this table.
Administrative MySQL Command
以下是一些重要的 MySQL 命令的列表，您将随时使用它们来处理 MySQL 数据库：
Here is the list of the important MySQL commands, which you will use time to time to work with MySQL database −
-
USE Databasename − This will be used to select a database in the MySQL workarea.
-
SHOW DATABASES − Lists out the databases that are accessible by the MySQL DBMS.
-
SHOW TABLES − Shows the tables in the database once a database has been selected with the use command.
-
SHOW COLUMNS FROM tablename: Shows the attributes, types of attributes, key information, whether NULL is permitted, defaults, and other information for a table.
-
SHOW INDEX FROM tablename − Presents the details of all indexes on the table, including the PRIMARY KEY.
-
SHOW TABLE STATUS LIKE tablename\G − Reports details of the MySQL DBMS performance and statistics.
在下一章中，我们将讨论如何在 MySQL 中使用 PHP 语法。
In the next chapter, we will discuss regarding how PHP Syntax is used in MySQL.
MySQL - PHP Syntax
MySQL 可与 PERL、C、C++、JAVA 和 PHP 等各种编程语言完美结合使用。在这些语言中，PHP 因其 Web 应用程序开发功能而最受欢迎。
MySQL works very well in combination of various programming languages like PERL, C, C++, JAVA and PHP. Out of these languages, PHP is the most popular one because of its web application development capabilities.
本教程着重于在 PHP 环境中使用 MySQL。如果您对带有 PERL 的 MySQL 感兴趣，那么您可以考虑阅读 PERL 教程。
This tutorial focuses heavily on using MySQL in a PHP environment. If you are interested in MySQL with PERL, then you can consider reading the PERL Tutorial.
PHP 提供了各种功能来访问 MySQL 数据库并在 MySQL 数据库中操作数据记录。您需要像调用任何其他 PHP 函数一样调用 PHP 函数。
PHP provides various functions to access the MySQL database and to manipulate the data records inside the MySQL database. You would require to call the PHP functions in the same way you call any other PHP function.
用于 MySQL 的 PHP 函数采用以下常规格式：
The PHP functions for use with MySQL have the following general format −
mysql_function(value,value,...);函数名的第二部分特定于函数，通常是一个描述函数执行操作的单词。以下是我们将在本教程中使用的两个函数：
The second part of the function name is specific to the function, usually a word that describes what the function does. The following are two of the functions, which we will use in our tutorial −
mysqli_connect($connect);
mysqli_query($connect,"SQL statement");以下示例显示 PHP 调用任何 MySQL 函数的通用语法。
The following example shows a generic syntax of PHP to call any MySQL function.
<html>
<head>
<title>PHP with MySQL</title>
</head>
<body>
<?php
$retval = mysql_function(value, [value,...]);
if( !$retval ) {
die ( "Error: a related error message" );
}
// Otherwise MySQL or PHP Statements
?>
</body>
</html>从下一章开始，我们将看到所有重要的 MySQL 功能以及 PHP。
Starting from the next chapter, we will see all the important MySQL functionality along with PHP.
MySQL - Connection
MySQL Connection Using MySQL Binary
你可以在命令提示符下使用 mysql 二进制文件建立 MySQL 数据库。
You can establish the MySQL database using the mysql binary at the command prompt.
Example
下面是一个从命令提示符连接到 MySQL 服务器的简单示例 −
Here is a simple example to connect to the MySQL server from the command prompt −
[root@host]# mysql -u root -p
Enter password:******这会为你提供一个 mysql> 命令提示符，你将可以在其中执行任意 SQL 命令。以下是上述命令的结果 −
This will give you the mysql> command prompt where you will be able to execute any SQL command. Following is the result of above command −
以下代码块显示了以上代码的结果 −
The following code block shows the result of above code −
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 2854760 to server version: 5.0.9
Type 'help;' or '\h' for help. Type '\c' to clear the buffer.在上述示例中，我们使用了 root 作为用户，但你也可以使用任何其他用户。任何用户都可以执行所有被允许执行的 SQL 操作。
In the above example, we have used root as a user but you can use any other user as well. Any user will be able to perform all the SQL operations, which are allowed to that user.
你可以随时使用 mysql> 提示符下的 exit 命令断开 MySQL 数据库连接。
You can disconnect from the MySQL database any time using the exit command at mysql> prompt.
mysql> exit
ByeMySQL Connection Using PHP Script
PHP 提供 mysql_connect() 函数来打开数据库连接。此函数接受五个参数，并在成功时返回一个 MySQL 链接标识符，在失败时返回 FALSE。
PHP provides mysql_connect() function to open a database connection. This function takes five parameters and returns a MySQL link identifier on success or FALSE on failure.
Syntax
connection mysql_connect(server,user,passwd,new_link,client_flag);你可以随时使用另一个 PHP 函数 mysql_close() 断开 MySQL 数据库连接。此函数接受单个参数，该参数是 mysql_connect() 函数返回的连接。
You can disconnect from the MySQL database anytime using another PHP function mysql_close(). This function takes a single parameter, which is a connection returned by the mysql_connect() function.
Syntax
bool mysql_close ( resource $link_identifier );如果未指定资源，则关闭上次打开的数据库。此函数会在成功关闭连接时返回 true，否则返回 false。
If a resource is not specified, then the last opened database is closed. This function returns true if it closes the connection successfully otherwise it returns false.
Example
尝试以下示例以连接到 MySQL 服务器 −
Try the following example to connect to a MySQL server −
<html>
<head>
<title>Connecting MySQL Server</title>
</head>
<body>
<?php
$dbhost = 'localhost:3306';
$dbuser = 'guest';
$dbpass = 'guest123';
$conn = mysql_connect($dbhost, $dbuser, $dbpass);
if(! $conn ) {
die('Could not connect: ' . mysql_error());
}
echo 'Connected successfully';
mysql_close($conn);
?>
</body>
</html>MySQL - Create Database
Create Database Using mysqladmin
您需要拥有特殊权限才能创建或删除 MySQL 数据库。因此，假设您有权访问 root 用户，则可以使用 mysql mysqladmin 二进制文件创建任何数据库。
You would need special privileges to create or to delete a MySQL database. So assuming you have access to the root user, you can create any database using the mysql mysqladmin binary.
Create a Database using PHP Script
PHP 使用 mysql_query 函数创建或删除 MySQL 数据库。此函数接受两个参数，并在成功时返回 TRUE，在失败时返回 FALSE。
PHP uses mysql_query function to create or delete a MySQL database. This function takes two parameters and returns TRUE on success or FALSE on failure.
Example
以下示例用于创建数据库 −
The following example to create a database −
<html>
<head>
<title>Creating MySQL Database</title>
</head>
<body>
<?php
$dbhost = 'localhost:3036';
$dbuser = 'root';
$dbpass = 'rootpassword';
$conn = mysql_connect($dbhost, $dbuser, $dbpass);
if(! $conn ) {
die('Could not connect: ' . mysql_error());
}
echo 'Connected successfully<br />';
$sql = 'CREATE DATABASE TUTORIALS';
$retval = mysql_query( $sql, $conn );
if(! $retval ) {
die('Could not create database: ' . mysql_error());
}
echo "Database TUTORIALS created successfully\n";
mysql_close($conn);
?>
</body>
</html>Drop MySQL Database
Drop a Database using mysqladmin
您将需要特殊权限来创建或删除 MySQL 数据库。因此，假设您可以访问 root 用户，那么可以使用 mysql mysqladmin 二进制文件创建任何数据库。
You would need special privileges to create or to delete a MySQL database. So, assuming you have access to the root user, you can create any database using the mysql mysqladmin binary.
删除任何数据库时要小心，因为这会让你失去数据库中所有可用数据。
Be careful while deleting any database because you will lose your all the data available in your database.
以下是一个示例，用于删除在上一个章节中创建的数据库 (TUTORIALS) −
Here is an example to delete a database(TUTORIALS) created in the previous chapter −
[root@host]# mysqladmin -u root -p drop TUTORIALS
Enter password:******这会给你一个警告，并会确认你是否真的想删除此数据库。
This will give you a warning and it will confirm if you really want to delete this database or not.
Dropping the database is potentially a very bad thing to do.
Any data stored in the database will be destroyed.
Do you really want to drop the 'TUTORIALS' database [y/N] y
Database "TUTORIALS" droppedDrop Database using PHP Script
PHP 使用 mysql_query 函数创建或删除 MySQL 数据库。此函数接受两个参数，并在成功时返回 TRUE，在失败时返回 FALSE。
PHP uses mysql_query function to create or delete a MySQL database. This function takes two parameters and returns TRUE on success or FALSE on failure.
Example
尝试以下示例来删除数据库 −
Try the following example to delete a database −
<html>
<head>
<title>Deleting MySQL Database</title>
</head>
<body>
<?php
$dbhost = 'localhost:3036';
$dbuser = 'root';
$dbpass = 'rootpassword';
$conn = mysql_connect($dbhost, $dbuser, $dbpass);
if(! $conn ) {
die('Could not connect: ' . mysql_error());
}
echo 'Connected successfully<br />';
$sql = 'DROP DATABASE TUTORIALS';
$retval = mysql_query( $sql, $conn );
if(! $retval ) {
die('Could not delete database: ' . mysql_error());
}
echo "Database TUTORIALS deleted successfully\n";
mysql_close($conn);
?>
</body>
</html>WARNING − 在使用 PHP 脚本删除数据库时，它不会提示你进行任何确认。因此在删除 MySQL 数据库时要小心。
WARNING − While deleting a database using the PHP script, it does not prompt you for any confirmation. So be careful while deleting a MySQL database.
Selecting MySQL Database
一旦连接到 MySQL 服务器，就需要选择一个数据库进行操作。这是因为 MySQL Server 可能有多个数据库可用。
Once you get connected with the MySQL server, it is required to select a database to work with. This is because there might be more than one database available with the MySQL Server.
Selecting MySQL Database from the Command Prompt
从 mysql> 提示符中选择数据库非常简单。你可以使用 SQL 命令 use 来选择数据库。
It is very simple to select a database from the mysql> prompt. You can use the SQL command use to select a database.
Example
这里有一个示例来选择名为 TUTORIALS 的数据库 −
Here is an example to select a database called TUTORIALS −
[root@host]# mysql -u root -p
Enter password:******
mysql> use TUTORIALS;
Database changed
mysql>现在，你已经选择了 TUTORIALS 数据库，并且所有后续操作都将在 TUTORIALS 数据库上执行。
Now, you have selected the TUTORIALS database and all the subsequent operations will be performed on the TUTORIALS database.
NOTE − 所有的数据库名称、表名、表字段名都区分大小写。因此，在提供任何 SQL 命令时，您必须使用适当的名称。
NOTE − All the database names, table names, table fields name are case sensitive. So you would have to use the proper names while giving any SQL command.
Selecting a MySQL Database Using PHP Script
PHP 提供功能 mysql_select_db 来选择数据库。它在成功时返回 TRUE，在失败时返回 FALSE。
PHP provides function mysql_select_db to select a database. It returns TRUE on success or FALSE on failure.
Example
以下示例展示如何选择数据库。
Here is an example showing you how to select a database.
<html>
<head>
<title>Selecting MySQL Database</title>
</head>
<body>
<?php
$dbhost = 'localhost:3036';
$dbuser = 'guest';
$dbpass = 'guest123';
$conn = mysql_connect($dbhost, $dbuser, $dbpass);
if(! $conn ) {
die('Could not connect: ' . mysql_error());
}
echo 'Connected successfully';
mysql_select_db( 'TUTORIALS' );
mysql_close($conn);
?>
</body>
</html>MySQL - Data Types
正确定义表中的字段对于数据库的整体优化很重要。您应该仅使用实际需要使用的字段类型和大小。例如，如果您知道只使用 2 个字符，则不要定义一个宽度为 10 个字符的字段。这些类型的字段（或列）在 type of data 中存储后也被称为数据类型。
Properly defining the fields in a table is important to the overall optimization of your database. You should use only the type and size of field you really need to use. For example, do not define a field 10 characters wide, if you know you are only going to use 2 characters. These type of fields (or columns) are also referred to as data types, after the type of data you will be storing in those fields.
MySQL 使用许多不同的数据类型，分为三类 −
MySQL uses many different data types broken into three categories −
-
Numeric
-
Date and Time
-
String Types.
现在我们详细讨论它们。
Let us now discuss them in detail.
Numeric Data Types
MySQL 使用所有标准 ANSI SQL 数值数据类型，因此如果您是从其他数据库系统转到 MySQL，这些定义对您来说很熟悉。
MySQL uses all the standard ANSI SQL numeric data types, so if you’re coming to MySQL from a different database system, these definitions will look familiar to you.
以下列表显示了常见数值数据类型及其说明 −
The following list shows the common numeric data types and their descriptions −
-
INT − A normal-sized integer that can be signed or unsigned. If signed, the allowable range is from -2147483648 to 2147483647. If unsigned, the allowable range is from 0 to 4294967295. You can specify a width of up to 11 digits.
-
TINYINT − A very small integer that can be signed or unsigned. If signed, the allowable range is from -128 to 127. If unsigned, the allowable range is from 0 to 255. You can specify a width of up to 4 digits.
-
SMALLINT − A small integer that can be signed or unsigned. If signed, the allowable range is from -32768 to 32767. If unsigned, the allowable range is from 0 to 65535. You can specify a width of up to 5 digits.
-
MEDIUMINT − A medium-sized integer that can be signed or unsigned. If signed, the allowable range is from -8388608 to 8388607. If unsigned, the allowable range is from 0 to 16777215. You can specify a width of up to 9 digits.
-
BIGINT − A large integer that can be signed or unsigned. If signed, the allowable range is from -9223372036854775808 to 9223372036854775807. If unsigned, the allowable range is from 0 to 18446744073709551615. You can specify a width of up to 20 digits.
-
FLOAT(M,D) − A floating-point number that cannot be unsigned. You can define the display length (M) and the number of decimals (D). This is not required and will default to 10,2, where 2 is the number of decimals and 10 is the total number of digits (including decimals). Decimal precision can go to 24 places for a FLOAT.
-
DOUBLE(M,D) − A double precision floating-point number that cannot be unsigned. You can define the display length (M) and the number of decimals (D). This is not required and will default to 16,4, where 4 is the number of decimals. Decimal precision can go to 53 places for a DOUBLE. REAL is a synonym for DOUBLE.
-
DECIMAL(M,D) − An unpacked floating-point number that cannot be unsigned. In the unpacked decimals, each decimal corresponds to one byte. Defining the display length (M) and the number of decimals (D) is required. NUMERIC is a synonym for DECIMAL.
Date and Time Types
MySQL 日期和时间数据类型如下 −
The MySQL date and time datatypes are as follows −
-
DATE − A date in YYYY-MM-DD format, between 1000-01-01 and 9999-12-31. For example, December 30th, 1973 would be stored as 1973-12-30.
-
DATETIME − A date and time combination in YYYY-MM-DD HH:MM:SS format, between 1000-01-01 00:00:00 and 9999-12-31 23:59:59. For example, 3:30 in the afternoon on December 30th, 1973 would be stored as 1973-12-30 15:30:00.
-
TIMESTAMP − A timestamp between midnight, January 1st, 1970 and sometime in 2037. This looks like the previous DATETIME format, only without the hyphens between numbers; 3:30 in the afternoon on December 30th, 1973 would be stored as 19731230153000 ( YYYYMMDDHHMMSS ).
-
TIME − Stores the time in a HH:MM:SS format.
-
YEAR(M) − Stores a year in a 2-digit or a 4-digit format. If the length is specified as 2 (for example YEAR(2)), YEAR can be between 1970 to 2069 (70 to 69). If the length is specified as 4, then YEAR can be 1901 to 2155. The default length is 4.
String Types
尽管数值和日期类型很有趣，但您存储的大部分数据将采用字符串格式。此列表描述了 MySQL 中常见的字符串数据类型。
Although the numeric and date types are fun, most data you’ll store will be in a string format. This list describes the common string datatypes in MySQL.
-
CHAR(M) − A fixed-length string between 1 and 255 characters in length (for example CHAR(5)), right-padded with spaces to the specified length when stored. Defining a length is not required, but the default is 1.
-
VARCHAR(M) − A variable-length string between 1 and 255 characters in length. For example, VARCHAR(25). You must define a length when creating a VARCHAR field.
-
BLOB or TEXT − A field with a maximum length of 65535 characters. BLOBs are "Binary Large Objects" and are used to store large amounts of binary data, such as images or other types of files. Fields defined as TEXT also hold large amounts of data. The difference between the two is that the sorts and comparisons on the stored data are case sensitive on BLOBs and are not case sensitive in TEXT fields. You do not specify a length with BLOB or TEXT.
-
TINYBLOB or TINYTEXT − A BLOB or TEXT column with a maximum length of 255 characters. You do not specify a length with TINYBLOB or TINYTEXT.
-
MEDIUMBLOB or MEDIUMTEXT − A BLOB or TEXT column with a maximum length of 16777215 characters. You do not specify a length with MEDIUMBLOB or MEDIUMTEXT.
-
LONGBLOB or LONGTEXT − A BLOB or TEXT column with a maximum length of 4294967295 characters. You do not specify a length with LONGBLOB or LONGTEXT.
-
ENUM − An enumeration, which is a fancy term for list. When defining an ENUM, you are creating a list of items from which the value must be selected (or it can be NULL). For example, if you wanted your field to contain "A" or "B" or "C", you would define your ENUM as ENUM ('A', 'B', 'C') and only those values (or NULL) could ever populate that field.
在下一章中，我们将讨论如何在 MySQL 中创建表。
In the next chapter, we will discuss how to create tables in MySQL.
Create MySQL Tables
首先，表格创建命令需要以下详细信息 -
To begin with, the table creation command requires the following details −
-
Name of the table
-
Name of the fields
-
Definitions for each field
Syntax
以下是一个用于创建 MySQL 表的通用 SQL 语法 −
Here is a generic SQL syntax to create a MySQL table −
CREATE TABLE table_name (column_name column_type);现在，我们在 TUTORIALS 数据库中创建以下表。
Now, we will create the following table in the TUTORIALS database.
create table tutorials_tbl(
tutorial_id INT NOT NULL AUTO_INCREMENT,
tutorial_title VARCHAR(100) NOT NULL,
tutorial_author VARCHAR(40) NOT NULL,
submission_date DATE,
PRIMARY KEY ( tutorial_id )
);此处，需要对几个项目进行说明 -
Here, a few items need explanation −
-
Field Attribute NOT NULL is being used because we do not want this field to be NULL. So, if a user will try to create a record with a NULL value, then MySQL will raise an error.
-
Field Attribute AUTO_INCREMENT tells MySQL to go ahead and add the next available number to the id field.
-
Keyword PRIMARY KEY is used to define a column as a primary key. You can use multiple columns separated by a comma to define a primary key.
Creating Tables from Command Prompt
很容易从 mysql> 提示符创建 MySQL 表。您将使用 SQL 命令 CREATE TABLE 来创建表。
It is easy to create a MySQL table from the mysql> prompt. You will use the SQL command CREATE TABLE to create a table.
Example
这是一个示例，它将创建 tutorials_tbl −
Here is an example, which will create tutorials_tbl −
root@host# mysql -u root -p
Enter password:*******
mysql> use TUTORIALS;
Database changed
mysql> CREATE TABLE tutorials_tbl(
-> tutorial_id INT NOT NULL AUTO_INCREMENT,
-> tutorial_title VARCHAR(100) NOT NULL,
-> tutorial_author VARCHAR(40) NOT NULL,
-> submission_date DATE,
-> PRIMARY KEY ( tutorial_id )
-> );
Query OK, 0 rows affected (0.16 sec)
mysql>NOTE - MySQL 在 SQL 命令末尾输入分号 (;) 之前不会终止命令。
NOTE − MySQL does not terminate a command until you give a semicolon (;) at the end of SQL command.
Creating Tables Using PHP Script
要在任何现有数据库中创建新表，您需要使用 PHP 函数 mysql_query() 。您将以正确的 SQL 命令作为其第二个参数来创建表。
To create new table in any existing database you would need to use PHP function mysql_query(). You will pass its second argument with a proper SQL command to create a table.
Example
以下程序是用 PHP 脚本创建表的示例 −
The following program is an example to create a table using PHP script −
<html>
<head>
<title>Creating MySQL Tables</title>
</head>
<body>
<?php
$dbhost = 'localhost:3036';
$dbuser = 'root';
$dbpass = 'rootpassword';
$conn = mysql_connect($dbhost, $dbuser, $dbpass);
if(! $conn ) {
die('Could not connect: ' . mysql_error());
}
echo 'Connected successfully<br />';
$sql = "CREATE TABLE tutorials_tbl( ".
"tutorial_id INT NOT NULL AUTO_INCREMENT, ".
"tutorial_title VARCHAR(100) NOT NULL, ".
"tutorial_author VARCHAR(40) NOT NULL, ".
"submission_date DATE, ".
"PRIMARY KEY ( tutorial_id )); ";
mysql_select_db( 'TUTORIALS' );
$retval = mysql_query( $sql, $conn );
if(! $retval ) {
die('Could not create table: ' . mysql_error());
}
echo "Table created successfully\n";
mysql_close($conn);
?>
</body>
</html>Drop MySQL Tables
删除现有的 MySQL 表格非常容易，但您在删除任何现有表格时需要非常小心，因为删除表格后丢失的数据将无法恢复。
It is very easy to drop an existing MySQL table, but you need to be very careful while deleting any existing table because the data lost will not be recovered after deleting a table.
Syntax
以下是删除 MySQL 表格的通用 SQL 语法 -
Here is a generic SQL syntax to drop a MySQL table −
DROP TABLE table_name ;Dropping Tables from the Command Prompt
要从命令提示符删除表格，我们需要在 mysql> 提示符处执行 DROP TABLE SQL 命令。
To drop tables from the command prompt, we need to execute the DROP TABLE SQL command at the mysql> prompt.
Dropping Tables Using PHP Script
要在任何数据库中删除现有表格，您需要使用 PHP 函数 mysql_query() 。您将其第二个参数与一个适当的 SQL 命令一起传递，以删除表格。
To drop an existing table in any database, you would need to use the PHP function mysql_query(). You will pass its second argument with a proper SQL command to drop a table.
Example
<html>
<head>
<title>Creating MySQL Tables</title>
</head>
<body>
<?php
$dbhost = 'localhost:3036';
$dbuser = 'root';
$dbpass = 'rootpassword';
$conn = mysql_connect($dbhost, $dbuser, $dbpass);
if(! $conn ) {
die('Could not connect: ' . mysql_error());
}
echo 'Connected successfully<br />';
$sql = "DROP TABLE tutorials_tbl";
mysql_select_db( 'TUTORIALS' );
$retval = mysql_query( $sql, $conn );
if(! $retval ) {
die('Could not delete table: ' . mysql_error());
}
echo "Table deleted successfully\n";
mysql_close($conn);
?>
</body>
</html>MySQL - Insert Query
要将数据插入 MySQL 表格，您需要使用 SQL INSERT INTO 命令。您可以使用 mysql> 提示符或使用任何像 PHP 这样的脚本将数据插入 MySQL 表格。
To insert data into a MySQL table, you would need to use the SQL INSERT INTO command. You can insert data into the MySQL table by using the mysql> prompt or by using any script like PHP.
Syntax
以下是 INSERT INTO 命令用于将数据插入 MySQL 表格的通用 SQL 语法 -
Here is a generic SQL syntax of INSERT INTO command to insert data into the MySQL table −
INSERT INTO table_name ( field1, field2,...fieldN )
VALUES
( value1, value2,...valueN );要插入字符串数据类型，需要将所有值放入双引号或单引号中。例如 "value" 。
To insert string data types, it is required to keep all the values into double or single quotes. For example "value".
Inserting Data from the Command Prompt
要从命令提示符插入数据，我们将使用 SQL INSERT INTO 命令将数据插入 MySQL 表格 tutorials_tbl。
To insert data from the command prompt, we will use SQL INSERT INTO command to insert data into MySQL table tutorials_tbl.
Example
以下示例将在 tutorials_tbl 表格中创建 3 条记录 -
The following example will create 3 records into tutorials_tbl table −
root@host# mysql -u root -p password;
Enter password:*******
mysql> use TUTORIALS;
Database changed
mysql> INSERT INTO tutorials_tbl
->(tutorial_title, tutorial_author, submission_date)
->VALUES
->("Learn PHP", "John Poul", NOW());
Query OK, 1 row affected (0.01 sec)
mysql> INSERT INTO tutorials_tbl
->(tutorial_title, tutorial_author, submission_date)
->VALUES
->("Learn MySQL", "Abdul S", NOW());
Query OK, 1 row affected (0.01 sec)
mysql> INSERT INTO tutorials_tbl
->(tutorial_title, tutorial_author, submission_date)
->VALUES
->("JAVA Tutorial", "Sanjay", '2007-05-06');
Query OK, 1 row affected (0.01 sec)
mysql>NOTE - 请注意所有箭头符号 (→) 不是 SQL 命令的一部分。它们表示一个新行，并且在命令的每行末尾不加分号时，它们会由 MySQL 提示符自动创建。
NOTE − Please note that all the arrow signs (→) are not a part of the SQL command. They are indicating a new line and they are created automatically by the MySQL prompt while pressing the enter key without giving a semicolon at the end of each line of the command.
在上述示例中，我们没有提供 tutorial_id，因为在创建表格时，我们为该字段给出了 AUTO_INCREMENT 选项。因此，MySQL 会自动插入这些 ID。此处， NOW() 是一个 MySQL 函数，它会返回当前日期和时间。
In the above example, we have not provided a tutorial_id because at the time of table creation, we had given AUTO_INCREMENT option for this field. So MySQL takes care of inserting these IDs automatically. Here, NOW() is a MySQL function, which returns the current date and time.
Inserting Data Using a PHP Script
您可以在 PHP 函数 mysql_query() 中使用相同的 SQL INSERT INTO 命令，将数据插入 MySQL 表格。
You can use the same SQL INSERT INTO command into the PHP function mysql_query() to insert data into a MySQL table.
Example
此示例会从用户那里获取三个参数，并将它们插入 MySQL 表格 -
This example will take three parameters from the user and will insert them into the MySQL table −
<html>
<head>
<title>Add New Record in MySQL Database</title>
</head>
<body>
<?php
if(isset($_POST['add'])) {
$dbhost = 'localhost:3036';
$dbuser = 'root';
$dbpass = 'rootpassword';
$conn = mysql_connect($dbhost, $dbuser, $dbpass);
if(! $conn ) {
die('Could not connect: ' . mysql_error());
}
if(! get_magic_quotes_gpc() ) {
$tutorial_title = addslashes ($_POST['tutorial_title']);
$tutorial_author = addslashes ($_POST['tutorial_author']);
} else {
$tutorial_title = $_POST['tutorial_title'];
$tutorial_author = $_POST['tutorial_author'];
}
$submission_date = $_POST['submission_date'];
$sql = "INSERT INTO tutorials_tbl ".
"(tutorial_title,tutorial_author, submission_date) "."VALUES ".
"('$tutorial_title','$tutorial_author','$submission_date')";
mysql_select_db('TUTORIALS');
$retval = mysql_query( $sql, $conn );
if(! $retval ) {
die('Could not enter data: ' . mysql_error());
}
echo "Entered data successfully\n";
mysql_close($conn);
} else {
?>
<form method = "post" action = "<?php $_PHP_SELF ?>">
<table width = "600" border = "0" cellspacing = "1" cellpadding = "2">
<tr>
<td width = "250">Tutorial Title</td>
<td>
<input name = "tutorial_title" type = "text" id = "tutorial_title">
</td>
</tr>
<tr>
<td width = "250">Tutorial Author</td>
<td>
<input name = "tutorial_author" type = "text" id = "tutorial_author">
</td>
</tr>
<tr>
<td width = "250">Submission Date [ yyyy-mm-dd ]</td>
<td>
<input name = "submission_date" type = "text" id = "submission_date">
</td>
</tr>
<tr>
<td width = "250"> </td>
<td> </td>
</tr>
<tr>
<td width = "250"> </td>
<td>
<input name = "add" type = "submit" id = "add" value = "Add Tutorial">
</td>
</tr>
</table>
</form>
<?php
}
?>
</body>
</html>在执行数据插入时，最好使用函数 get_magic_quotes_gpc() 来检查当前 magic quote 配置是否已设置。如果此函数返回 false，则使用函数 addslashes() 在引号前添加反斜杠。
While doing a data insert, it is best to use the function get_magic_quotes_gpc() to check if the current configuration for magic quote is set or not. If this function returns false, then use the function addslashes() to add slashes before the quotes.
您可以进行许多验证，以检查输入的数据是否正确，并可以采取适当的操作。
You can put many validations around to check if the entered data is correct or not and can take the appropriate action.
MySQL - Select Query
SQL SELECT 命令用于从 MySQL 数据库中获取数据。您可以在 mysql> 提示符以及任何像 PHP 这样的脚本中使用此命令。
The SQL SELECT command is used to fetch data from the MySQL database. You can use this command at mysql> prompt as well as in any script like PHP.
Syntax
以下是用于从 MySQL 表格中获取数据的 SELECT 命令的通用 SQL 语法 -
Here is generic SQL syntax of SELECT command to fetch data from the MySQL table −
SELECT field1, field2,...fieldN
FROM table_name1, table_name2...
[WHERE Clause]
[OFFSET M ][LIMIT N]-
You can use one or more tables separated by comma to include various conditions using a WHERE clause, but the WHERE clause is an optional part of the SELECT command.
-
You can fetch one or more fields in a single SELECT command.
-
You can specify star (*) in place of fields. In this case, SELECT will return all the fields.
-
You can specify any condition using the WHERE clause.
-
You can specify an offset using OFFSET from where SELECT will start returning records. By default, the offset starts at zero.
-
You can limit the number of returns using the LIMIT attribute.
Fetching Data from a Command Prompt
这将使用 SQL SELECT 命令从 MySQL 表 tutorials_tbl 中获取数据。
This will use SQL SELECT command to fetch data from the MySQL table tutorials_tbl.
Example
以下示例将返回 tutorials_tbl 表中的所有记录 -
The following example will return all the records from the tutorials_tbl table −
root@host# mysql -u root -p password;
Enter password:*******
mysql> use TUTORIALS;
Database changed
mysql> SELECT * from tutorials_tbl
+-------------+----------------+-----------------+-----------------+
| tutorial_id | tutorial_title | tutorial_author | submission_date |
+-------------+----------------+-----------------+-----------------+
| 1 | Learn PHP | John Poul | 2007-05-21 |
| 2 | Learn MySQL | Abdul S | 2007-05-21 |
| 3 | JAVA Tutorial | Sanjay | 2007-05-21 |
+-------------+----------------+-----------------+-----------------+
3 rows in set (0.01 sec)
mysql>Fetching Data Using a PHP Script
您可以将相同的 SQL SELECT 命令用于 PHP 函数 mysql_query() 。此函数用于执行 SQL 命令，然后稍后可以使用另一个 PHP 函数 mysql_fetch_array() 来获取所有选定的数据。此函数将行作为关联数组、数字数组或两者返回。如果不再有行，则此函数将返回 FALSE。
You can use the same SQL SELECT command into a PHP function mysql_query(). This function is used to execute the SQL command and then later another PHP function mysql_fetch_array() can be used to fetch all the selected data. This function returns the row as an associative array, a numeric array, or both. This function returns FALSE if there are no more rows.
以下程序是一个简单的示例，它将展示如何从 tutorials_tbl 表中获取/显示记录。
The following program is a simple example which will show how to fetch / display records from the tutorials_tbl table.
Example
以下代码块将显示 tutorials_tbl 表中的所有记录。
The following code block will display all the records from the tutorials_tbl table.
<?php
$dbhost = 'localhost:3036';
$dbuser = 'root';
$dbpass = 'rootpassword';
$conn = mysql_connect($dbhost, $dbuser, $dbpass);
if(! $conn ) {
die('Could not connect: ' . mysql_error());
}
$sql = 'SELECT tutorial_id, tutorial_title, tutorial_author, submission_date FROM tutorials_tbl';
mysql_select_db('TUTORIALS');
$retval = mysql_query( $sql, $conn );
if(! $retval ) {
die('Could not get data: ' . mysql_error());
}
while($row = mysql_fetch_array($retval, MYSQL_ASSOC)) {
echo "Tutorial ID :{$row['tutorial_id']} <br> ".
"Title: {$row['tutorial_title']} <br> ".
"Author: {$row['tutorial_author']} <br> ".
"Submission Date : {$row['submission_date']} <br> ".
"--------------------------------<br>";
}
echo "Fetched data successfully\n";
mysql_close($conn);
?>行的内容分配给变量 $row，然后打印该行中的值。
The content of the rows is assigned to the variable $row and the values in that row are then printed.
NOTE − 始终记住，当您想要直接将数组值插入到字符串中时，要放置大括号。
NOTE − Always remember to put curly brackets when you want to insert an array value directly into a string.
在上面的示例中，常量 MYSQL_ASSOC 用作 PHP 函数 mysql_fetch_array() 的第二个参数，以便它将行作为关联数组返回。使用关联数组，您可以通过使用字段名称代替使用索引来访问字段。
In the above example, the constant MYSQL_ASSOC is used as the second argument to the PHP function mysql_fetch_array(), so that it returns the row as an associative array. With an associative array you can access the field by using their name instead of using the index.
PHP 提供了另一个名为 mysql_fetch_assoc() 的函数，它还将行作为关联数组返回。
PHP provides another function called mysql_fetch_assoc(), which also returns the row as an associative array.
Example
以下示例使用 mysql_fetch_assoc() 函数显示 tutorial_tbl 表中的所有记录。
The following example to display all the records from the tutorial_tbl table using mysql_fetch_assoc() function.
<?php
$dbhost = 'localhost:3036';
$dbuser = 'root';
$dbpass = 'rootpassword';
$conn = mysql_connect($dbhost, $dbuser, $dbpass);
if(! $conn ) {
die('Could not connect: ' . mysql_error());
}
$sql = 'SELECT tutorial_id, tutorial_title, tutorial_author, submission_date
FROM tutorials_tbl';
mysql_select_db('TUTORIALS');
$retval = mysql_query( $sql, $conn );
if(! $retval ) {
die('Could not get data: ' . mysql_error());
}
while($row = mysql_fetch_assoc($retval)) {
echo "Tutorial ID :{$row['tutorial_id']} <br> ".
"Title: {$row['tutorial_title']} <br> ".
"Author: {$row['tutorial_author']} <br> ".
"Submission Date : {$row['submission_date']} <br> ".
"--------------------------------<br>";
}
echo "Fetched data successfully\n";
mysql_close($conn);
?>您还可以将常量 MYSQL_NUM 用作 PHP 函数 mysql_fetch_array() 的第二个参数。这将导致函数返回带有数字索引的数组。
You can also use the constant MYSQL_NUM as the second argument to the PHP function mysql_fetch_array(). This will cause the function to return an array with the numeric index.
Example
尝试以下示例，以使用 MYSQL_NUM 参数显示 tutorials_tbl 表中的所有记录。
Try out the following example to display all the records from tutorials_tbl table using the MYSQL_NUM argument.
<?php
$dbhost = 'localhost:3036';
$dbuser = 'root';
$dbpass = 'rootpassword';
$conn = mysql_connect($dbhost, $dbuser, $dbpass);
if(! $conn ) {
die('Could not connect: ' . mysql_error());
}
$sql = 'SELECT tutorial_id, tutorial_title, tutorial_author, submission_date
FROM tutorials_tbl';
mysql_select_db('TUTORIALS');
$retval = mysql_query( $sql, $conn );
if(! $retval ) {
die('Could not get data: ' . mysql_error());
}
while($row = mysql_fetch_array($retval, MYSQL_NUM)) {
echo "Tutorial ID :{$row[0]} <br> ".
"Title: {$row[1]} <br> ".
"Author: {$row[2]} <br> ".
"Submission Date : {$row[3]} <br> ".
"--------------------------------<br>";
}
echo "Fetched data successfully\n";
mysql_close($conn);
?>以上所有三个示例将产生相同的结果。
All the above three examples will produce the same result.
Releasing Memory
释放游标内存是一个好习惯，它应该在每个 SELECT 语句的末尾进行。可以使用 PHP 函数 mysql_free_result() 来完成此操作。以下程序是一个示例，展示如何使用它。
It is a good practice to release cursor memory at the end of each SELECT statement. This can be done by using the PHP function mysql_free_result(). The following program is the example to show how it should be used.
Example
尝试以下示例 -
Try out the following example −
<?php
$dbhost = 'localhost:3036';
$dbuser = 'root';
$dbpass = 'rootpassword';
$conn = mysql_connect($dbhost, $dbuser, $dbpass);
if(! $conn ) {
die('Could not connect: ' . mysql_error());
}
$sql = 'SELECT tutorial_id, tutorial_title, tutorial_author, submission_date
FROM tutorials_tbl';
mysql_select_db('TUTORIALS');
$retval = mysql_query( $sql, $conn );
if(! $retval ) {
die('Could not get data: ' . mysql_error());
}
while($row = mysql_fetch_array($retval, MYSQL_NUM)) {
echo "Tutorial ID :{$row[0]} <br> ".
"Title: {$row[1]} <br> ".
"Author: {$row[2]} <br> ".
"Submission Date : {$row[3]} <br> ".
"--------------------------------<br>";
}
mysql_free_result($retval);
echo "Fetched data successfully\n";
mysql_close($conn);
?>在获取数据时，您可以编写任意复杂的代码，但过程将保持与上面提到的相同。
While fetching data, you can write as complex a code as you like, but the procedure will remain the same as mentioned above.
MySQL - WHERE Clause
我们已经看到了 SQL SELECT 命令，用于从 MySQL 表获取数据。我们可以使用一个称为 WHERE Clause 的条件子句来过滤结果。使用此 WHERE 子句，我们可以指定选择条件以从表中选择所需的记录。
We have seen the SQL SELECT command to fetch data from a MySQL table. We can use a conditional clause called the WHERE Clause to filter out the results. Using this WHERE clause, we can specify a selection criteria to select the required records from a table.
Syntax
以下代码块有使用 WHERE 子句的 SELECT 命令的通用 SQL 语法，用于从 MySQL 表中获取数据 -
The following code block has a generic SQL syntax of the SELECT command with the WHERE clause to fetch data from the MySQL table −
SELECT field1, field2,...fieldN table_name1, table_name2...
[WHERE condition1 [AND [OR]] condition2.....-
You can use one or more tables separated by a comma to include various conditions using a WHERE clause, but the WHERE clause is an optional part of the SELECT command.
-
You can specify any condition using the WHERE clause.
-
You can specify more than one condition using the AND or the OR operators.
-
A WHERE clause can be used along with DELETE or UPDATE SQL command also to specify a condition.
WHERE 子句的工作方式类似于任何编程语言中的 if condition 。此子句用于将给定值与 MySQL 表中可用的字段值进行比较。如果外部的给定值等于 MySQL 表中可用的字段值，则它会返回该行。
The WHERE clause works like an if condition in any programming language. This clause is used to compare the given value with the field value available in a MySQL table. If the given value from outside is equal to the available field value in the MySQL table, then it returns that row.
以下是该 WHERE 子句中可以使用的运算符列表。
Here is the list of operators, which can be used with the WHERE clause.
假设字段 A 持有 10 且字段 B 持有 20，那么 -
Assume field A holds 10 and field B holds 20, then −
当您想要从表中获取所选行时，WHERE 子句非常有用，尤其是在使用 MySQL Join 时。联接将在另一章中讨论。
The WHERE clause is very useful when you want to fetch the selected rows from a table, especially when you use the MySQL Join. Joins are discussed in another chapter.
使用 Primary Key 搜索记录是一种常见的做法，可以使搜索更快。
It is a common practice to search for records using the Primary Key to make the search faster.
如果给定条件与表中的任何记录都不匹配，则该查询将不会返回任何行。
If the given condition does not match any record in the table, then the query would not return any row.
Fetching Data from the Command Prompt
这将使用带有 WHERE 子句的 SQL SELECT 命令从 MySQL 表中获取所选数据 - tutorials_tbl 。
This will use the SQL SELECT command with the WHERE clause to fetch the selected data from the MySQL table – tutorials_tbl.
Example
以下示例将返回 tutorials_tbl 表中所有作者名为 Sanjay 的记录。
The following example will return all the records from the tutorials_tbl table for which the author name is Sanjay.
root@host# mysql -u root -p password;
Enter password:*******
mysql> use TUTORIALS;
Database changed
mysql> SELECT * from tutorials_tbl WHERE tutorial_author = 'Sanjay';
+-------------+----------------+-----------------+-----------------+
| tutorial_id | tutorial_title | tutorial_author | submission_date |
+-------------+----------------+-----------------+-----------------+
| 3 | JAVA Tutorial | Sanjay | 2007-05-21 |
+-------------+----------------+-----------------+-----------------+
1 rows in set (0.01 sec)
mysql>除非对字符串执行 LIKE 比较，否则该比较不区分大小写。您可以使用 BINARY 关键字使搜索区分大小写，如下所示 -
Unless performing a LIKE comparison on a string, the comparison is not case sensitive. You can make your search case sensitive by using the BINARY keyword as follows −
root@host# mysql -u root -p password;
Enter password:*******
mysql> use TUTORIALS;
Database changed
mysql> SELECT * from tutorials_tbl \
WHERE BINARY tutorial_author = 'sanjay';
Empty set (0.02 sec)
mysql>Fetching Data Using a PHP Script
您可以将带有 WHERE 子句的 SQL SELECT 命令与 PHP 函数 mysql_query() 中使用。该函数用于执行 SQL 命令，稍后可使用另一个 PHP 函数 mysql_fetch_array() 获取所有所选数据。该函数将行返回为关联数组、数字数组或两者。如果不再有行，则此函数将返回 FALSE。
You can use the same SQL SELECT command with the WHERE CLAUSE into the PHP function mysql_query(). This function is used to execute the SQL command and later another PHP function mysql_fetch_array() can be used to fetch all the selected data. This function returns a row as an associative array, a numeric array, or both. This function returns FALSE if there are no more rows.
Example
以下示例将返回 tutorials_tbl 表中所有作者名为 Sanjay 的记录 -
The following example will return all the records from the tutorials_tbl table for which the author name is Sanjay −
<?php
$dbhost = 'localhost:3036';
$dbuser = 'root';
$dbpass = 'rootpassword';
$conn = mysql_connect($dbhost, $dbuser, $dbpass);
if(! $conn ) {
die('Could not connect: ' . mysql_error());
}
$sql = 'SELECT tutorial_id, tutorial_title,
tutorial_author, submission_date
FROM tutorials_tbl
WHERE tutorial_author = "Sanjay"';
mysql_select_db('TUTORIALS');
$retval = mysql_query( $sql, $conn );
if(! $retval ) {
die('Could not get data: ' . mysql_error());
}
while($row = mysql_fetch_array($retval, MYSQL_ASSOC)) {
echo "Tutorial ID :{$row['tutorial_id']} <br> ".
"Title: {$row['tutorial_title']} <br> ".
"Author: {$row['tutorial_author']} <br> ".
"Submission Date : {$row['submission_date']} <br> ".
"--------------------------------<br>";
}
echo "Fetched data successfully\n";
mysql_close($conn);
?>MySQL - UPDATE Query
可能需要修改 MySQL 表中的现有数据。您可以使用 SQL UPDATE 命令执行此操作。这将修改任何 MySQL 字段的任何字段值。
There may be a requirement where the existing data in a MySQL table needs to be modified. You can do so by using the SQL UPDATE command. This will modify any field value of any MySQL table.
Syntax
以下代码块具有修改 MySQL 表中的数据的 UPDATE 命令的通用 SQL 语法 -
The following code block has a generic SQL syntax of the UPDATE command to modify the data in the MySQL table −
UPDATE table_name SET field1 = new-value1, field2 = new-value2
[WHERE Clause]-
You can update one or more field altogether.
-
You can specify any condition using the WHERE clause.
-
You can update the values in a single table at a time.
当您想要更新表中的选定行时，WHERE 子句非常有用。
The WHERE clause is very useful when you want to update the selected rows in a table.
Updating Data from the Command Prompt
这将使用带 WHERE 子句的 SQL UPDATE 命令来更新 MySQL 表 tutorials_tbl 中选定的数据。
This will use the SQL UPDATE command with the WHERE clause to update the selected data in the MySQL table tutorials_tbl.
Example
以下示例将更新教程 ID 为 3 的记录的 tutorial_title 字段。
The following example will update the tutorial_title field for a record having the tutorial_id as 3.
root@host# mysql -u root -p password;
Enter password:*******
mysql> use TUTORIALS;
Database changed
mysql> UPDATE tutorials_tbl
-> SET tutorial_title = 'Learning JAVA'
-> WHERE tutorial_id = 3;
Query OK, 1 row affected (0.04 sec)
Rows matched: 1 Changed: 1 Warnings: 0
mysql>Updating Data Using a PHP Script
您可以将带或不带 WHERE 子句的 SQL UPDATE 命令一起用于 PHP 函数 - mysql_query() 。该函数将以与在 mysql> 提示符下执行它类似的方式执行 SQL 命令。
You can use the SQL UPDATE command with or without the WHERE CLAUSE into the PHP function – mysql_query(). This function will execute the SQL command in a similar way it is executed at the mysql> prompt.
Example
以下示例将更新教程 ID 为 3 的记录的 tutorial_title 字段。
The following example to update the tutorial_title field for a record having tutorial_id as 3.
<?php
$dbhost = 'localhost:3036';
$dbuser = 'root';
$dbpass = 'rootpassword';
$conn = mysql_connect($dbhost, $dbuser, $dbpass);
if(! $conn ) {
die('Could not connect: ' . mysql_error());
}
$sql = 'UPDATE tutorials_tbl
SET tutorial_title="Learning JAVA"
WHERE tutorial_id=3';
mysql_select_db('TUTORIALS');
$retval = mysql_query( $sql, $conn );
if(! $retval ) {
die('Could not update data: ' . mysql_error());
}
echo "Updated data successfully\n";
mysql_close($conn);
?>MySQL - DELETE Query
如果您想从任何 MySQL 表中删除记录，那么您可以使用 SQL 命令 DELETE FROM 。您可以在 mysql> 提示符处以及在 PHP 等任何脚本中使用此命令。
If you want to delete a record from any MySQL table, then you can use the SQL command DELETE FROM. You can use this command at the mysql> prompt as well as in any script like PHP.
Syntax
以下代码块是 DELETE 命令的通用 SQL 语法，用于从 MySQL 表中删除数据。
The following code block has a generic SQL syntax of the DELETE command to delete data from a MySQL table.
DELETE FROM table_name [WHERE Clause]-
If the WHERE clause is not specified, then all the records will be deleted from the given MySQL table.
-
You can specify any condition using the WHERE clause.
-
You can delete records in a single table at a time.
当你想删除表中的选定行时，WHERE 子句非常有用。
The WHERE clause is very useful when you want to delete selected rows in a table.
Deleting Data from the Command Prompt
这将使用带有 WHERE 子句的 SQL DELETE 命令将所选数据删除到 MySQL 表中 - tutorials_tbl 。
This will use the SQL DELETE command with the WHERE clause to delete selected data into the MySQL table – tutorials_tbl.
Example
以下示例将从教程 ID 为 3 的 tutorial_tbl 中删除一条记录。
The following example will delete a record from the tutorial_tbl whose tutorial_id is 3.
root@host# mysql -u root -p password;
Enter password:*******
mysql> use TUTORIALS;
Database changed
mysql> DELETE FROM tutorials_tbl WHERE tutorial_id=3;
Query OK, 1 row affected (0.23 sec)
mysql>Deleting Data Using a PHP Script
您可以使用带或不带 WHERE 子句的 SQL DELETE 命令作为 PHP 函数 – mysql_query() 。此函数将以与在 mysql> 提示符处执行相同的方式执行 SQL 命令。
You can use the SQL DELETE command with or without the WHERE CLAUSE into the PHP function – mysql_query(). This function will execute the SQL command in the same way as it is executed at the mysql> prompt.
Example
尝试以下示例以删除教程 ID 为 3 的 tutorial_tbl 中的一条记录。
Try the following example to delete a record from the tutorial_tbl whose tutorial_id is 3.
<?php
$dbhost = 'localhost:3036';
$dbuser = 'root';
$dbpass = 'rootpassword';
$conn = mysql_connect($dbhost, $dbuser, $dbpass);
if(! $conn ) {
die('Could not connect: ' . mysql_error());
}
$sql = 'DELETE FROM tutorials_tbl WHERE tutorial_id = 3';
mysql_select_db('TUTORIALS');
$retval = mysql_query( $sql, $conn );
if(! $retval ) {
die('Could not delete data: ' . mysql_error());
}
echo "Deleted data successfully\n";
mysql_close($conn);
?>MySQL - LIKE Clause
我们已经见过 SQL SELECT 命令以从 MySQL 表中获取数据。我们还可以使用一个称为 WHERE 子句的条件子句来选择所需的记录。
We have seen the SQL SELECT command to fetch data from the MySQL table. We can also use a conditional clause called as the WHERE clause to select the required records.
带有“等于”符号 (=) 的 WHERE 子句可以正常工作，在这种情况下我们希望进行精确匹配。例如“tutorial_author = 'Sanjay'”。但可能会有一些要求，即我们希望过滤出教程作者名称应包含“jay”的所有结果。这可以使用 SQL LIKE Clause 和 WHERE 子句一起处理。
A WHERE clause with the ‘equal to’ sign (=) works fine where we want to do an exact match. Like if "tutorial_author = 'Sanjay'". But there may be a requirement where we want to filter out all the results where tutorial_author name should contain "jay". This can be handled using SQL LIKE Clause along with the WHERE clause.
如果 SQL LIKE 子句与 % 字符一起使用，则它将像一个元字符（ ) as in UNIX, while listing out all the files or directories at the command prompt. Without a % character, the LIKE clause is very same as the *equal to 符号和 WHERE 子句一起）。
If the SQL LIKE clause is used along with the % character, then it will work like a meta character () as in UNIX, while listing out all the files or directories at the command prompt. Without a % character, the LIKE clause is very same as the *equal to sign along with the WHERE clause.
Syntax
以下代码块具有 SELECT 命令的通用 SQL 语法以及 LIKE 子句，以从 MySQL 表中获取数据。
The following code block has a generic SQL syntax of the SELECT command along with the LIKE clause to fetch data from a MySQL table.
SELECT field1, field2,...fieldN table_name1, table_name2...
WHERE field1 LIKE condition1 [AND [OR]] filed2 = 'somevalue'-
You can specify any condition using the WHERE clause.
-
You can use the LIKE clause along with the WHERE clause.
-
You can use the LIKE clause in place of the equals to sign.
-
When LIKE is used along with % sign then it will work like a meta character search.
-
You can specify more than one condition using AND or OR operators.
-
A WHERE…LIKE clause can be used along with DELETE or UPDATE SQL command also to specify a condition.
Using the LIKE clause at the Command Prompt
这将使用具有 WHERE…LIKE 子句的 SQL SELECT 命令从 MySQL 表中获取选定的数据 – tutorials_tbl 。
This will use the SQL SELECT command with the WHERE…LIKE clause to fetch the selected data from the MySQL table – tutorials_tbl.
Example
以下示例将返回 tutorials_tbl 表中作者名称以 jay 结尾的所有记录 −
The following example will return all the records from the tutorials_tbl table for which the author name ends with jay −
root@host# mysql -u root -p password;
Enter password:*******
mysql> use TUTORIALS;
Database changed
mysql> SELECT * from tutorials_tbl
-> WHERE tutorial_author LIKE '%jay';
+-------------+----------------+-----------------+-----------------+
| tutorial_id | tutorial_title | tutorial_author | submission_date |
+-------------+----------------+-----------------+-----------------+
| 3 | JAVA Tutorial | Sanjay | 2007-05-21 |
+-------------+----------------+-----------------+-----------------+
1 rows in set (0.01 sec)
mysql>Using LIKE clause inside PHP Script
您可以在 PHP 函数 – mysql_query() 中使用 WHERE…LIKE 子句的类似语法。此函数用于执行 SQL 命令，稍后另一个 PHP 函数 – mysql_fetch_array() 可用于获取所有选定的数据（如果 WHERE…LIKE 子句与 SELECT 命令一起使用）。
You can use similar syntax of the WHERE…LIKE clause into the PHP function – mysql_query(). This function is used to execute the SQL command and later another PHP function – mysql_fetch_array() can be used to fetch all the selected data, if the WHERE…LIKE clause is used along with the SELECT command.
但是，如果正在使用 WHERE…LIKE 子句 DELETE 或 UPDATE 命令，则不需要进一步的 PHP 函数调用。
But if the WHERE…LIKE clause is being used with the DELETE or UPDATE command, then no further PHP function call is required.
Example
尝试以下示例以返回 tutorials_tbl 表中作者名称包含 jay 的所有记录 −
Try out the following example to return all the records from the tutorials_tbl table for which the author name contains jay −
<?php
$dbhost = 'localhost:3036';
$dbuser = 'root';
$dbpass = 'rootpassword';
$conn = mysql_connect($dbhost, $dbuser, $dbpass);
if(! $conn ) {
die('Could not connect: ' . mysql_error());
}
$sql = 'SELECT tutorial_id, tutorial_title,
tutorial_author, submission_date
FROM tutorials_tbl
WHERE tutorial_author LIKE "%jay%"';
mysql_select_db('TUTORIALS');
$retval = mysql_query( $sql, $conn );
if(! $retval ) {
die('Could not get data: ' . mysql_error());
}
while($row = mysql_fetch_array($retval, MYSQL_ASSOC)) {
echo "Tutorial ID :{$row['tutorial_id']} <br> ".
"Title: {$row['tutorial_title']} <br> ".
"Author: {$row['tutorial_author']} <br> ".
"Submission Date : {$row['submission_date']} <br> ".
"--------------------------------<br>";
}
echo "Fetched data successfully\n";
mysql_close($conn);
?>MySQL - Sorting Results
我们已经见过 SQL SELECT 命令以从 MySQL 表中获取数据。当您选择行时，MySQL 服务器可以按任何顺序自由返回它们，除非您通过说明如何对结果排序来指示它这样做。但是，您可以通过添加 ORDER BY 子句来对结果集进行排序，该子句指定您要排序的列或多列。
We have seen the SQL SELECT command to fetch data from a MySQL table. When you select rows, the MySQL server is free to return them in any order, unless you instruct it otherwise by saying how to sort the result. But, you sort a result set by adding an ORDER BY clause that names the column or columns which you want to sort.
Syntax
以下代码块是 SELECT 命令的一个通用 SQL 语法，以及 ORDER BY 子句以对 MySQL 表中的数据进行排序。
The following code block is a generic SQL syntax of the SELECT command along with the ORDER BY clause to sort the data from a MySQL table.
SELECT field1, field2,...fieldN table_name1, table_name2...
ORDER BY field1, [field2...] [ASC [DESC]]-
You can sort the returned result on any field, if that field is being listed out.
-
You can sort the result on more than one field.
-
You can use the keyword ASC or DESC to get result in ascending or descending order. By default, it’s the ascending order.
-
You can use the WHERE…LIKE clause in the usual way to put a condition.
Using ORDER BY clause at the Command Prompt
这将使用具有 ORDER BY 子句的 SQL SELECT 命令从 MySQL 表中获取数据 – tutorials_tbl 。
This will use the SQL SELECT command with the ORDER BY clause to fetch data from the MySQL table – tutorials_tbl.
Example
尝试以下示例，它以升序返回结果。
Try out the following example, which returns the result in an ascending order.
root@host# mysql -u root -p password;
Enter password:*******
mysql> use TUTORIALS;
Database changed
mysql> SELECT * from tutorials_tbl ORDER BY tutorial_author ASC
+-------------+----------------+-----------------+-----------------+
| tutorial_id | tutorial_title | tutorial_author | submission_date |
+-------------+----------------+-----------------+-----------------+
| 2 | Learn MySQL | Abdul S | 2007-05-24 |
| 1 | Learn PHP | John Poul | 2007-05-24 |
| 3 | JAVA Tutorial | Sanjay | 2007-05-06 |
+-------------+----------------+-----------------+-----------------+
3 rows in set (0.42 sec)
mysql>验证按升序列出的所有作者姓名。
Verify all the author names that are listed out in the ascending order.
Using ORDER BY clause inside a PHP Script
您可以在 PHP 函数中使用 ORDER BY 子句 mysql_query() 中的类似语法。该函数用于执行 SQL 命令，然后可以使用另一个 PHP 函数 mysql_fetch_array() 来获取所有选定的数据。
You can use a similar syntax of the ORDER BY clause into the PHP function – mysql_query(). This function is used to execute the SQL command and later another PHP function mysql_fetch_array() can be used to fetch all the selected data.
Example
尝试以下示例，其中按照教程作者以降序返回结果。
Try out the following example, which returns the result in a descending order of the tutorial authors.
<?php
$dbhost = 'localhost:3036';
$dbuser = 'root';
$dbpass = 'rootpassword';
$conn = mysql_connect($dbhost, $dbuser, $dbpass);
if(! $conn ) {
die('Could not connect: ' . mysql_error());
}
$sql = 'SELECT tutorial_id, tutorial_title,
tutorial_author, submission_date
FROM tutorials_tbl
ORDER BY tutorial_author DESC';
mysql_select_db('TUTORIALS');
$retval = mysql_query( $sql, $conn );
if(! $retval ) {
die('Could not get data: ' . mysql_error());
}
while($row = mysql_fetch_array($retval, MYSQL_ASSOC)) {
echo "Tutorial ID :{$row['tutorial_id']} <br> ".
"Title: {$row['tutorial_title']} <br> ".
"Author: {$row['tutorial_author']} <br> ".
"Submission Date : {$row['submission_date']} <br> ".
"--------------------------------<br>";
}
echo "Fetched data successfully\n";
mysql_close($conn);
?>Using MySQl Joins
在之前的章节中，我们一次从一个表中获取数据。这对于简单的数据获取已经足够了，但是在大多数现实世界的 MySQL 用法中，您通常需要在单个查询中从多个表中获取数据。
In the previous chapters, we were getting data from one table at a time. This is good enough for simple takes, but in most of the real world MySQL usages, you will often need to get data from multiple tables in a single query.
您可以在单个 SQL 查询中使用多个表。在 MySQL 中进行连接操作是指将两个或更多个表组合成一个表。
You can use multiple tables in your single SQL query. The act of joining in MySQL refers to smashing two or more tables into a single table.
您可以在 SELECT、UPDATE 和 DELETE 语句中使用 JOINS 来连接 MySQL 表。我们还将看到 LEFT JOIN 的一个示例，它不同于简单的 MySQL JOIN。
You can use JOINS in the SELECT, UPDATE and DELETE statements to join the MySQL tables. We will see an example of the LEFT JOIN also which is different from the simple MySQL JOIN.
Using Joins at the Command Prompt
假设我们在 TUTORIALS 中有两个表 tcount_tbl 和 tutorials_tbl 。现在，请查看以下给出的示例 -
Assume we have two tables tcount_tbl and tutorials_tbl, in TUTORIALS. Now take a look at the examples given below −
Example
以下示例 -
The following examples −
root@host# mysql -u root -p password;
Enter password:*******
mysql> use TUTORIALS;
Database changed
mysql> SELECT * FROM tcount_tbl;
+-----------------+----------------+
| tutorial_author | tutorial_count |
+-----------------+----------------+
| mahran | 20 |
| mahnaz | NULL |
| Jen | NULL |
| Gill | 20 |
| John Poul | 1 |
| Sanjay | 1 |
+-----------------+----------------+
6 rows in set (0.01 sec)
mysql> SELECT * from tutorials_tbl;
+-------------+----------------+-----------------+-----------------+
| tutorial_id | tutorial_title | tutorial_author | submission_date |
+-------------+----------------+-----------------+-----------------+
| 1 | Learn PHP | John Poul | 2007-05-24 |
| 2 | Learn MySQL | Abdul S | 2007-05-24 |
| 3 | JAVA Tutorial | Sanjay | 2007-05-06 |
+-------------+----------------+-----------------+-----------------+
3 rows in set (0.00 sec)
mysql>现在，我们可以编写一条 SQL 查询来连接这两个表。该查询将从表 tutorials_tbl 中选择所有作者，并将从 tcount_tbl 中选取相应的教程数量。
Now we can write an SQL query to join these two tables. This query will select all the authors from table tutorials_tbl and will pick up the corresponding number of tutorials from the tcount_tbl.
mysql> SELECT a.tutorial_id, a.tutorial_author, b.tutorial_count
-> FROM tutorials_tbl a, tcount_tbl b
-> WHERE a.tutorial_author = b.tutorial_author;
+-------------+-----------------+----------------+
| tutorial_id | tutorial_author | tutorial_count |
+-------------+-----------------+----------------+
| 1 | John Poul | 1 |
| 3 | Sanjay | 1 |
+-------------+-----------------+----------------+
2 rows in set (0.01 sec)
mysql>Using Joins in a PHP Script
您可以在 PHP 脚本中使用上述任何 SQL 查询。您只需将 SQL 查询传递给 PHP 函数 mysql_query() ，然后您将以常规方式获取结果。
You can use any of the above-mentioned SQL query in the PHP script. You only need to pass the SQL query into the PHP function mysql_query() and then you will fetch results in the usual way.
Example
以下示例 -
The following example −
<?php
$dbhost = 'localhost:3036';
$dbuser = 'root';
$dbpass = 'rootpassword';
$conn = mysql_connect($dbhost, $dbuser, $dbpass);
if(! $conn ) {
die('Could not connect: ' . mysql_error());
}
$sql = 'SELECT a.tutorial_id, a.tutorial_author, b.tutorial_count
FROM tutorials_tbl a, tcount_tbl b
WHERE a.tutorial_author = b.tutorial_author';
mysql_select_db('TUTORIALS');
$retval = mysql_query( $sql, $conn );
if(! $retval ) {
die('Could not get data: ' . mysql_error());
}
while($row = mysql_fetch_array($retval, MYSQL_ASSOC)) {
echo "Author:{$row['tutorial_author']} <br> ".
"Count: {$row['tutorial_count']} <br> ".
"Tutorial ID: {$row['tutorial_id']} <br> ".
"--------------------------------<br>";
}
echo "Fetched data successfully\n";
mysql_close($conn);
?>MySQL LEFT JOIN
MySQL 左连接不同于简单连接。MySQL LEFT JOIN 会更加考虑表中左侧的列。
A MySQL left join is different from a simple join. A MySQL LEFT JOIN gives some extra consideration to the table that is on the left.
如果我执行 LEFT JOIN ，我将获得所有匹配的记录，并且另外，我将获得连接表左侧中每个不匹配记录的额外记录：从而确保（在我的示例中）每个 AUTHOR 都被提及。
If I do a LEFT JOIN, I get all the records that match in the same way and IN ADDITION I get an extra record for each unmatched record in the left table of the join: thus ensuring (in my example) that every AUTHOR gets a mention.
Example
尝试以下示例来了解 LEFT JOIN。
Try the following example to understand the LEFT JOIN.
root@host# mysql -u root -p password;
Enter password:*******
mysql> use TUTORIALS;
Database changed
mysql> SELECT a.tutorial_id, a.tutorial_author, b.tutorial_count
-> FROM tutorials_tbl a LEFT JOIN tcount_tbl b
-> ON a.tutorial_author = b.tutorial_author;
+-------------+-----------------+----------------+
| tutorial_id | tutorial_author | tutorial_count |
+-------------+-----------------+----------------+
| 1 | John Poul | 1 |
| 2 | Abdul S | NULL |
| 3 | Sanjay | 1 |
+-------------+-----------------+----------------+
3 rows in set (0.02 sec)您需要做更多的练习以熟悉 JOINS。这是一个稍微有点复杂的 MySQL/SQL 概念，并且在实际操作时会变得更加清晰。
You would need to do more practice to become familiar with JOINS. This is slightly a bit complex concept in MySQL/SQL and will become more clear while doing real examples.
Handling MySQL NULL Values
我们已经看到了 SQL SELECT 命令以及 WHERE 子句，用于从 MySQL 表中获取数据，但是当我们尝试给出一个条件时，该条件将字段或列值与 NULL 进行比较，它不能正常工作。
We have seen the SQL SELECT command along with the WHERE clause to fetch data from a MySQL table, but when we try to give a condition, which compares the field or the column value to NULL, it does not work properly.
为了处理这种情况，MySQL 提供了三个运算符 -
To handle such a situation, MySQL provides three operators −
-
IS NULL − This operator returns true, if the column value is NULL.
-
IS NOT NULL − This operator returns true, if the column value is not NULL.
-
<⇒ − This operator compares values, which (unlike the = operator) is true even for two NULL values.
涉及 NULL 的条件是特殊的。不能使用 = NULL 或 != NULL 来查找列中的 NULL 值。这种比较始终失败，因为无法判断它们是真还是假。有时，甚至 NULL = NULL 会失败。
The conditions involving NULL are special. You cannot use = NULL or != NULL to look for NULL values in columns. Such comparisons always fail because it is impossible to tell whether they are true or not. Sometimes, even NULL = NULL fails.
要查找存在或不存在 NULL 的列，请使用 IS NULL 或 IS NOT NULL 。
To look for columns that are or are not NULL, use IS NULL or IS NOT NULL.
Using NULL values at the Command Prompt
假设 TUTORIALS 数据库中有一个名为 tcount_tbl 的表，它包含两列，即 tutorial_author 和 tutorial_count ，其中 tutorial_count 为 NULL 表示该值未知。
Assume that there is a table called tcount_tbl in the TUTORIALS database and it contains two columns namely tutorial_author and tutorial_count, where a NULL tutorial_count indicates that the value is unknown.
Example
尝试以下示例：
Try the following examples −
root@host# mysql -u root -p password;
Enter password:*******
mysql> use TUTORIALS;
Database changed
mysql> create table tcount_tbl
-> (
-> tutorial_author varchar(40) NOT NULL,
-> tutorial_count INT
-> );
Query OK, 0 rows affected (0.05 sec)
mysql> INSERT INTO tcount_tbl
-> (tutorial_author, tutorial_count) values ('mahran', 20);
mysql> INSERT INTO tcount_tbl
-> (tutorial_author, tutorial_count) values ('mahnaz', NULL);
mysql> INSERT INTO tcount_tbl
-> (tutorial_author, tutorial_count) values ('Jen', NULL);
mysql> INSERT INTO tcount_tbl
-> (tutorial_author, tutorial_count) values ('Gill', 20);
mysql> SELECT * from tcount_tbl;
+-----------------+----------------+
| tutorial_author | tutorial_count |
+-----------------+----------------+
| mahran | 20 |
| mahnaz | NULL |
| Jen | NULL |
| Gill | 20 |
+-----------------+----------------+
4 rows in set (0.00 sec)
mysql>可以看到， = 和 != 不适用于 NULL 值，如下所示：
You can see that = and != do not work with NULL values as follows −
mysql> SELECT * FROM tcount_tbl WHERE tutorial_count = NULL;
Empty set (0.00 sec)
mysql> SELECT * FROM tcount_tbl WHERE tutorial_count != NULL;
Empty set (0.01 sec)要查找 tutorial_count 列存在或不存在的记录，应按以下程序中所示编写查询。
To find the records where the tutorial_count column is or is not NULL, the queries should be written as shown in the following program.
mysql> SELECT * FROM tcount_tbl
-> WHERE tutorial_count IS NULL;
+-----------------+----------------+
| tutorial_author | tutorial_count |
+-----------------+----------------+
| mahnaz | NULL |
| Jen | NULL |
+-----------------+----------------+
2 rows in set (0.00 sec)
mysql> SELECT * from tcount_tbl
-> WHERE tutorial_count IS NOT NULL;
+-----------------+----------------+
| tutorial_author | tutorial_count |
+-----------------+----------------+
| mahran | 20 |
| Gill | 20 |
+-----------------+----------------+
2 rows in set (0.00 sec)Handling NULL Values in a PHP Script
可以使用 if…else 条件根据 NULL 值准备查询。
You can use the if…else condition to prepare a query based on the NULL value.
Example
以下示例从外部获取 tutorial_count ，然后将其与表中可用的值进行比较。
The following example takes the tutorial_count from outside and then compares it with the value available in the table.
<?php
$dbhost = 'localhost:3036';
$dbuser = 'root';
$dbpass = 'rootpassword';
$conn = mysql_connect($dbhost, $dbuser, $dbpass);
if(! $conn ) {
die('Could not connect: ' . mysql_error());
}
if( isset($tutorial_count )) {
$sql = 'SELECT tutorial_author, tutorial_count
FROM tcount_tbl
WHERE tutorial_count = $tutorial_count';
} else {
$sql = 'SELECT tutorial_author, tutorial_count
FROM tcount_tbl
WHERE tutorial_count IS $tutorial_count';
}
mysql_select_db('TUTORIALS');
$retval = mysql_query( $sql, $conn );
if(! $retval ) {
die('Could not get data: ' . mysql_error());
}
while($row = mysql_fetch_array($retval, MYSQL_ASSOC)) {
echo "Author:{$row['tutorial_author']} <br> ".
"Count: {$row['tutorial_count']} <br> ".
"--------------------------------<br>";
}
echo "Fetched data successfully\n";
mysql_close($conn);
?>MySQL - Regexps
已经看到 MySQL 模式匹配与 LIKE …% 。MySQL 支持基于正则表达式和 REGEXP 运算符的另一种类型的模式匹配操作。如果您了解 PHP 或 PERL，那么这很容易理解，因为这种匹配与那些编写正则表达式的脚本相同。
You have seen MySQL pattern matching with LIKE …%. MySQL supports another type of pattern matching operation based on the regular expressions and the REGEXP operator. If you are aware of PHP or PERL, then it is very simple for you to understand because this matching is same like those scripting the regular expressions.
以下是模式表，可与 REGEXP 运算符一起使用。
Following is the table of pattern, which can be used along with the REGEXP operator.
Examples
现在基于上表可以设计出各种类型的 SQL 查询以满足要求。在此，我列出一些供了解。
Now based on above table, you can device various type of SQL queries to meet your requirements. Here, I am listing a few for your understanding.
考虑有一个表名为 person_tbl ，并且有一个字段名为 name ：
Consider we have a table called person_tbl and it is having a field called name −
查找所有以 'st' 开头的名称的查询：
Query to find all the names starting with 'st' −
mysql> SELECT name FROM person_tbl WHERE name REGEXP '^st';查找所有以 'ok' 结尾的名称的查询：
Query to find all the names ending with 'ok' −
mysql> SELECT name FROM person_tbl WHERE name REGEXP 'ok$';查找所有包含 'mar' 的名称的查询：
Query to find all the names, which contain 'mar' −
mysql> SELECT name FROM person_tbl WHERE name REGEXP 'mar';查找所有以元音字母开头并以 'ok' 结尾的名称的查询：
Query to find all the names starting with a vowel and ending with 'ok' −
mysql> SELECT FirstName FROM intque.person_tbl WHERE FirstName REGEXP '^[aeiou].*ok$';MySQL - Transactions
事务是一组顺序的数据库操作，执行时就好像它是单个工作单元一样。换句话说，除非组内的每个操作都成功，否则事务永远不会完成。如果事务中的任何操作失败，整个事务都将失败。
A transaction is a sequential group of database manipulation operations, which is performed as if it were one single work unit. In other words, a transaction will never be complete unless each individual operation within the group is successful. If any operation within the transaction fails, the entire transaction will fail.
实际上，您会将许多 SQL 查询合并到一个组中，并将它们全部作为一个事务的一部分一起执行。
Practically, you will club many SQL queries into a group and you will execute all of them together as a part of a transaction.
Properties of Transactions
事务具有以下四个标准属性，通常用缩写 ACID 表示：
Transactions have the following four standard properties, usually referred to by the acronym ACID −
-
Atomicity − This ensures that all operations within the work unit are completed successfully; otherwise, the transaction is aborted at the point of failure and previous operations are rolled back to their former state.
-
Consistency − This ensures that the database properly changes states upon a successfully committed transaction.
-
Isolation − This enables transactions to operate independently on and transparent to each other.
-
Durability − This ensures that the result or effect of a committed transaction persists in case of a system failure.
在 MySQL 中，事务以语句 BEGIN WORK 开始，以 COMMIT 或 ROLLBACK 语句结束。开始语句和结束语句之间的 SQL 命令构成事务的主体。
In MySQL, the transactions begin with the statement BEGIN WORK and end with either a COMMIT or a ROLLBACK statement. The SQL commands between the beginning and ending statements form the bulk of the transaction.
COMMIT and ROLLBACK
这两个关键字 Commit 和 Rollback 主要用于 MySQL 事务。
These two keywords Commit and Rollback are mainly used for MySQL Transactions.
-
When a successful transaction is completed, the COMMIT command should be issued so that the changes to all involved tables will take effect.
-
If a failure occurs, a ROLLBACK command should be issued to return every table referenced in the transaction to its previous state.
你可以通过设置名为 AUTOCOMMIT 的会话变量来控制事务的行为。如果 AUTOCOMMIT 设置为 1（默认值），那么每个 SQL 语句（在事务中或不在事务中）都被视为一个完整的事务，并且在完成时默认提交。
You can control the behavior of a transaction by setting session variable called AUTOCOMMIT. If AUTOCOMMIT is set to 1 (the default), then each SQL statement (within a transaction or not) is considered a complete transaction and committed by default when it finishes.
当 AUTOCOMMIT 设置为 0 时，通过发出 SET AUTOCOMMIT = 0 命令，一系列后续语句将充当一个事务，并且没有任何活动被提交，直到发出显式的 COMMIT 语句。
When AUTOCOMMIT is set to 0, by issuing the SET AUTOCOMMIT = 0 command, the subsequent series of statements acts like a transaction and no activities are committed until an explicit COMMIT statement is issued.
你可以使用 mysql_query() 函数在 PHP 中执行这些 SQL 命令。
You can execute these SQL commands in PHP by using the mysql_query() function.
A Generic Example on Transaction
这系列事件与使用的编程语言无关。你可以在用于创建应用程序的任何语言中创建逻辑路径。
This sequence of events is independent of the programming language used. The logical path can be created in whichever language you use to create your application.
你可以使用 mysql_query() 函数在 PHP 中执行这些 SQL 命令。
You can execute these SQL commands in PHP by using the mysql_query() function.
-
Begin transaction by issuing the SQL command BEGIN WORK.
-
Issue one or more SQL commands like SELECT, INSERT, UPDATE or DELETE.
-
Check if there is no error and everything is according to your requirement.
-
If there is any error, then issue a ROLLBACK command, otherwise issue a COMMIT command.
Transaction-Safe Table Types in MySQL
你不能直接使用事务，但对于某些异常情况，你可以这样做。然而，它们并不能确保安全和稳定。如果你计划在你的 MySQL 编程中使用事务，那么你需要以一种特殊的方式创建你的表。支持事务的表类型有很多，但最流行的一类是 InnoDB 。
You cannot use transactions directly, but for certain exceptions you can. However, they are not safe and guaranteed. If you plan to use transactions in your MySQL programming, then you need to create your tables in a special way. There are many types of tables, which support transactions, but the most popular one is InnoDB.
支持 InnoDB 表需要你在从源代码编译 MySQL 时使用一个特定的编译参数。如果你的 MySQL 版本不支持 InnoDB，请要求你的互联网服务提供商构建一个支持 InnoDB 表类型的 MySQL 版本，或针对 Windows 或 Linux/UNIX 下载并安装 MySQL-Max Binary Distribution ，并在开发环境中使用该表类型。
Support for InnoDB tables requires a specific compilation parameter when compiling MySQL from the source. If your MySQL version does not have InnoDB support, ask your Internet Service Provider to build a version of MySQL with support for InnoDB table types or download and install the MySQL-Max Binary Distribution for Windows or Linux/UNIX and work with the table type in a development environment.
如果你的 MySQL 安装支持 InnoDB 表，则只需向表创建语句中添加一个 TYPE = InnoDB 定义。
If your MySQL installation supports InnoDB tables, simply add a TYPE = InnoDB definition to the table creation statement.
例如，以下代码创建了一个名为 tcount_tbl 的 InnoDB 表 −
For example, the following code creates an InnoDB table called tcount_tbl −
root@host# mysql -u root -p password;
Enter password:*******
mysql> use TUTORIALS;
Database changed
mysql> create table tcount_tbl
-> (
-> tutorial_author varchar(40) NOT NULL,
-> tutorial_count INT
-> ) TYPE = InnoDB;
Query OK, 0 rows affected (0.05 sec)关于 InnoDB 的更多详细信息，你可以点击以下链接 − InnoDB
For more details on InnoDB, you can click on the following link −InnoDB
你可以使用其他表格类型，例如 GEMINI 或 BDB ，但这取决于你的安装是否支持这两种表格类型。
You can use other table types like GEMINI or BDB, but it depends on your installation, whether it supports these two table types or not.
MySQL - ALTER Command
当你想更改表格名称、表格字段或添加或删除表格中的现有列时，MySQL ALTER 命令非常有用。
The MySQL ALTER command is very useful when you want to change a name of your table, any table field or if you want to add or delete an existing column in a table.
让我们从创建名为 testalter_tbl 的表格开始。
Let us begin with the creation of a table called testalter_tbl.
root@host# mysql -u root -p password;
Enter password:*******
mysql> use TUTORIALS;
Database changed
mysql> create table testalter_tbl
-> (
-> i INT,
-> c CHAR(1)
-> );
Query OK, 0 rows affected (0.05 sec)
mysql> SHOW COLUMNS FROM testalter_tbl;
+-------+---------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+---------+------+-----+---------+-------+
| i | int(11) | YES | | NULL | |
| c | char(1) | YES | | NULL | |
+-------+---------+------+-----+---------+-------+
2 rows in set (0.00 sec)Dropping, Adding or Repositioning a Column
如果你想删除 MySQL 表格中的一个现有列 i，那么你将使用 DROP 子句连同 ALTER 命令，如下所示：
If you want to drop an existing column i from the above MySQL table, then you will use the DROP clause along with the ALTER command as shown below −
mysql> ALTER TABLE testalter_tbl DROP i;如果该列是表格中唯一剩下的列， DROP 子句将无法使用。
A DROP clause will not work if the column is the only one left in the table.
要添加一个列，请使用 ADD 并指定该列的定义。以下语句将 i 列还原到 testalter_tbl：
To add a column, use ADD and specify the column definition. The following statement restores the i column to the testalter_tbl −
mysql> ALTER TABLE testalter_tbl ADD i INT;发出此语句之后，testalter 将包含创建该表格时拥有的相同的两列，但不会具有相同的结构。这是因为默认情况下会将新列添加到该表格的末尾。因此，即使 i 最初是 mytbl 中的第一列，现在它也是最后一列。
After issuing this statement, testalter will contain the same two columns that it had when you first created the table, but will not have the same structure. This is because there are new columns that are added to the end of the table by default. So even though i originally was the first column in mytbl, now it is the last one.
mysql> SHOW COLUMNS FROM testalter_tbl;
+-------+---------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+---------+------+-----+---------+-------+
| c | char(1) | YES | | NULL | |
| i | int(11) | YES | | NULL | |
+-------+---------+------+-----+---------+-------+
2 rows in set (0.00 sec)要指示你希望表格内有某一特殊位置的列，请使用 FIRST 将其设为第一列，或使用 AFTER col_name ，指示在 col_name 后放置新列。
To indicate that you want a column at a specific position within the table, either use FIRST to make it the first column or AFTER col_name to indicate that the new column should be placed after the col_name.
使用 SHOW COLUMNS 尝试以下 ALTER TABLE 语句，每个语句之后使用 SHOW COLUMNS ，了解每个语句的作用：
Try the following ALTER TABLE statements, using SHOW COLUMNS after each one to see what effect each one has −
ALTER TABLE testalter_tbl DROP i;
ALTER TABLE testalter_tbl ADD i INT FIRST;
ALTER TABLE testalter_tbl DROP i;
ALTER TABLE testalter_tbl ADD i INT AFTER c;FIRST 和 AFTER 说明符仅适用于 ADD 子句。这意味着，如果你要在表格中重新定位现有列，则必须先 DROP 它，然后在新的位置 ADD 它。
The FIRST and AFTER specifiers work only with the ADD clause. This means that if you want to reposition an existing column within a table, you first must DROP it and then ADD it at the new position.
Altering (Changing) a Column Definition or a Name
要更改列的定义，请使用 MODIFY 或 CHANGE 子句连同 ALTER 命令。
To change a column’s definition, use MODIFY or CHANGE clause along with the ALTER command.
例如，要将列 c 从 CHAR(1) 更改为 CHAR(10)，你可以使用以下命令：
For example, to change column c from CHAR(1) to CHAR(10), you can use the following command −
mysql> ALTER TABLE testalter_tbl MODIFY c CHAR(10);使用 CHANGE 时，语法稍微有些不同。在 CHANGE 关键字之后，你命名你要更改的列，然后指定新定义，其中包括新名称。
With CHANGE, the syntax is a bit different. After the CHANGE keyword, you name the column you want to change, then specify the new definition, which includes the new name.
尝试以下示例 -
Try out the following example −
mysql> ALTER TABLE testalter_tbl CHANGE i j BIGINT;如果你现在使用 CHANGE 将 j 从 BIGINT 转换回 INT 而无需更改该列名称，则语句将如下所示：
If you now use CHANGE to convert j from BIGINT back to INT without changing the column name, the statement will be as shown below −
mysql> ALTER TABLE testalter_tbl CHANGE j j INT;The Effect of ALTER TABLE on Null and Default Value Attributes — 如果你 MODIFY 或 CHANGE 一个列，你还可以指定该列是否可以包含 NULL 值以及它的默认值是多少。事实上，如果你不这样做，MySQL 会自动为这些属性分配值。
The Effect of ALTER TABLE on Null and Default Value Attributes − When you MODIFY or CHANGE a column, you can also specify whether or not the column can contain NULL values and what its default value is. In fact, if you don’t do this, MySQL automatically assigns values for these attributes.
以下代码块是一个示例，其中 NOT NULL 列的默认值为 100。
The following code block is an example, where the NOT NULL column will have the value as 100 by default.
mysql> ALTER TABLE testalter_tbl
-> MODIFY j BIGINT NOT NULL DEFAULT 100;如果你不使用上述命令，那么 MySQL 就会用 NULL 值填充所有这些列。
If you don’t use the above command, then MySQL will fill up NULL values in all the columns.
Altering (Changing) a Column’s Default Value
你可以使用 ALTER 命令更改任何列的默认值。
You can change a default value for any column by using the ALTER command.
试试以下示例。
Try out the following example.
mysql> ALTER TABLE testalter_tbl ALTER i SET DEFAULT 1000;
mysql> SHOW COLUMNS FROM testalter_tbl;
+-------+---------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+---------+------+-----+---------+-------+
| c | char(1) | YES | | NULL | |
| i | int(11) | YES | | 1000 | |
+-------+---------+------+-----+---------+-------+
2 rows in set (0.00 sec)使用 DROP 子句和 ALTER 命令可以从任何列中删除默认约束。
You can remove the default constraint from any column by using DROP clause along with the ALTER command.
mysql> ALTER TABLE testalter_tbl ALTER i DROP DEFAULT;
mysql> SHOW COLUMNS FROM testalter_tbl;
+-------+---------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+---------+------+-----+---------+-------+
| c | char(1) | YES | | NULL | |
| i | int(11) | YES | | NULL | |
+-------+---------+------+-----+---------+-------+
2 rows in set (0.00 sec)Altering (Changing) a Table Type
可以使用 TYPE 子句结合 ALTER 命令来使用表类型。尝试以下示例将 testalter_tbl 更改为 MYISAM 表类型。
You can use a table type by using the TYPE clause along with the ALTER command. Try out the following example to change the testalter_tbl to MYISAM table type.
要找出表的当前类型，请使用 SHOW TABLE STATUS 语句。
To find out the current type of a table, use the SHOW TABLE STATUS statement.
mysql> ALTER TABLE testalter_tbl TYPE = MYISAM;
mysql> SHOW TABLE STATUS LIKE 'testalter_tbl'\G
*************************** 1. row ****************
Name: testalter_tbl
Type: MyISAM
Row_format: Fixed
Rows: 0
Avg_row_length: 0
Data_length: 0
Max_data_length: 25769803775
Index_length: 1024
Data_free: 0
Auto_increment: NULL
Create_time: 2007-06-03 08:04:36
Update_time: 2007-06-03 08:04:36
Check_time: NULL
Create_options:
Comment:
1 row in set (0.00 sec)Renaming (Altering) a Table
要重命名表，请使用 RENAME 的 ALTER TABLE 语句选项。
To rename a table, use the RENAME option of the ALTER TABLE statement.
尝试以下示例将 testalter_tbl 重命名为 alter_tbl 。
Try out the following example to rename testalter_tbl to alter_tbl.
mysql> ALTER TABLE testalter_tbl RENAME TO alter_tbl;可以使用 ALTER 命令来创建和删除 MySQL 文件上的 INDEX 命令。我们将在下一章详细讨论此命令。
You can use the ALTER command to create and drop the INDEX command on a MySQL file. We will discuss in detail about this command in the next chapter.
MySQL - INDEXES
数据库索引是一种数据结构，可以提高表中操作的速度。可以使用一个或多个列创建索引，既可以快速随机查找，也可以有效地对记录访问进行排序。
A database index is a data structure that improves the speed of operations in a table. Indexes can be created using one or more columns, providing the basis for both rapid random lookups and efficient ordering of access to records.
在创建索引时，应考虑将使用哪些列来创建 SQL 查询，以及在这些列上创建一或多个索引。
While creating index, it should be taken into consideration which all columns will be used to make SQL queries and create one or more indexes on those columns.
实际上，索引也是一种表，它保留主键或索引字段以及指向实际表中每个记录的指针。
Practically, indexes are also a type of tables, which keep primary key or index field and a pointer to each record into the actual table.
用户无法看到索引，它们仅用于加快查询速度，并且数据库搜索引擎将使用它们来快速查找记录。
The users cannot see the indexes, they are just used to speed up queries and will be used by the Database Search Engine to locate records very fast.
对于有索引的表，INSERT 和 UPDATE 语句需要更多时间，而 SELECT 语句在这些表上会变快。原因是，在执行插入或更新时，数据库需要同时插入或更新索引值。
The INSERT and UPDATE statements take more time on tables having indexes, whereas the SELECT statements become fast on those tables. The reason is that while doing insert or update, a database needs to insert or update the index values as well.
Simple and Unique Index
可以在表上创建唯一索引。唯一索引意味着，两行不能有相同的索引值。以下是在表上创建索引的语法。
You can create a unique index on a table. A unique index means that two rows cannot have the same index value. Here is the syntax to create an Index on a table.
CREATE UNIQUE INDEX index_name ON table_name ( column1, column2,...);可以使用一列或多列创建索引。
You can use one or more columns to create an index.
例如，我们可以使用 tutorial_author 在 tutorials_tbl 上创建索引。
For example, we can create an index on tutorials_tbl using tutorial_author.
CREATE UNIQUE INDEX AUTHOR_INDEX ON tutorials_tbl (tutorial_author)可以在表上创建简单索引。只需从用于创建简单索引的查询中忽略 UNIQUE 关键字。简单索引允许表中有重复值。
You can create a simple index on a table. Just omit the UNIQUE keyword from the query to create a simple index. A Simple index allows duplicate values in a table.
如果您想按降序对某列中的值进行索引，您可以在列名后添加保留字 DESC。
If you want to index the values in a column in a descending order, you can add the reserved word DESC after the column name.
mysql> CREATE UNIQUE INDEX AUTHOR_INDEX ON tutorials_tbl (tutorial_author DESC)ALTER command to add and drop INDEX
有四类用于向表中添加索引的语句 −
There are four types of statements for adding indexes to a table −
-
ALTER TABLE tbl_name ADD PRIMARY KEY (column_list) − This statement adds a PRIMARY KEY, which means that the indexed values must be unique and cannot be NULL.
-
ALTER TABLE tbl_name ADD UNIQUE index_name (column_list) − This statement creates an index for which the values must be unique (except for the NULL values, which may appear multiple times).
-
ALTER TABLE tbl_name ADD INDEX index_name (column_list) − This adds an ordinary index in which any value may appear more than once.
-
ALTER TABLE tbl_name ADD FULLTEXT index_name (column_list) − This creates a special FULLTEXT index that is used for text-searching purposes.
以下代码块是一个在现有表中添加索引的示例。
The following code block is an example to add index in an existing table.
mysql> ALTER TABLE testalter_tbl ADD INDEX (c);可以使用 DROP 子句结合 ALTER 命令删除任何 INDEX。
You can drop any INDEX by using the DROP clause along with the ALTER command.
尝试以下示例来删除上面创建的索引。
Try out the following example to drop the above-created index.
mysql> ALTER TABLE testalter_tbl DROP INDEX (c);你可以使用 DROP 子句和 ALTER 命令来删除任何索引。
You can drop any INDEX by using the DROP clause along with the ALTER command.
ALTER Command to add and drop the PRIMARY KEY
你也可以用相同方式添加主键。但请确保主键对非 NULL 列有效。
You can add a primary key as well in the same way. But make sure the Primary Key works on columns, which are NOT NULL.
以下代码块是一个在现有表中添加主键的示例。这将首先创建一个非 NULL 列，然后将其添加为主键。
The following code block is an example to add the primary key in an existing table. This will make a column NOT NULL first and then add it as a primary key.
mysql> ALTER TABLE testalter_tbl MODIFY i INT NOT NULL;
mysql> ALTER TABLE testalter_tbl ADD PRIMARY KEY (i);你可以使用 ALTER 命令来删除主键，如下所示：
You can use the ALTER command to drop a primary key as follows −
mysql> ALTER TABLE testalter_tbl DROP PRIMARY KEY;要删除一个不是主键的索引，你必须指定索引名称。
To drop an index that is not a PRIMARY KEY, you must specify the index name.
Displaying INDEX Information
你可以使用 \s0 命令列出与表关联的所有索引。垂直格式输出（由 \G 指定）通常适用于此语句，以避免换行过长。
You can use the SHOW INDEX command to list out all the indexes associated with a table. The vertical-format output (specified by \G) often is useful with this statement, to avoid a long line wraparound −
尝试以下示例 -
Try out the following example −
mysql> SHOW INDEX FROM table_name\G
........MySQL - Temporary Tables
在某些情况下，临时表可能对保存临时数据非常有用。应该了解关于临时表的最重要的事情是，在当前客户端会话终止时，这些表将被删除。
The temporary tables could be very useful in some cases to keep temporary data. The most important thing that should be known for temporary tables is that they will be deleted when the current client session terminates.
What are Temporary Tables?
临时表在 MySQL 版本 3.23 中添加。如果你使用的 MySQL 版本低于 3.23，你不能使用临时表，但你可以使用 \s1。
Temporary tables were added in the MySQL Version 3.23. If you use an older version of MySQL than 3.23, you cannot use the temporary tables, but you can use Heap Tables.
如前所述，临时表只会持续到会话结束为止。如果您在 PHP 脚本中运行代码，那么临时表将在脚本执行完毕后自动销毁。如果您通过 MySQL 客户端程序连接到 MySQL 数据库服务器，那么该临时表将一直存在到您关闭客户端或手动销毁表为止。
As stated earlier, temporary tables will only last as long as the session is alive. If you run the code in a PHP script, the temporary table will be destroyed automatically when the script finishes executing. If you are connected to the MySQL database server through the MySQL client program, then the temporary table will exist until you close the client or manually destroy the table.
Example
以下程序是一个显示如何使用临时表的示例。相同的代码可以在 PHP 脚本中使用 \s2 函数。
The following program is an example showing you the usage of the temporary table. The same code can be used in PHP scripts using the mysql_query() function.
mysql> CREATE TEMPORARY TABLE SalesSummary (
-> product_name VARCHAR(50) NOT NULL
-> , total_sales DECIMAL(12,2) NOT NULL DEFAULT 0.00
-> , avg_unit_price DECIMAL(7,2) NOT NULL DEFAULT 0.00
-> , total_units_sold INT UNSIGNED NOT NULL DEFAULT 0
);
Query OK, 0 rows affected (0.00 sec)
mysql> INSERT INTO SalesSummary
-> (product_name, total_sales, avg_unit_price, total_units_sold)
-> VALUES
-> ('cucumber', 100.25, 90, 2);
mysql> SELECT * FROM SalesSummary;
+--------------+-------------+----------------+------------------+
| product_name | total_sales | avg_unit_price | total_units_sold |
+--------------+-------------+----------------+------------------+
| cucumber | 100.25 | 90.00 | 2 |
+--------------+-------------+----------------+------------------+
1 row in set (0.00 sec)当你发出 \s3 命令时，你的临时表将不会在列表中列出。现在，如果你退出 MySQL 会话，然后发出 \s4 命令，那么你将在数据库中找不到任何可用数据。即使你的临时表也不存在。
When you issue a SHOW TABLES command, then your temporary table would not be listed out in the list. Now, if you will log out of the MySQL session and then you will issue a SELECT command, then you will find no data available in the database. Even your temporary table will not exist.
Dropping Temporary Tables
默认情况下，当你数据库连接终止时，MySQL 会删除所有临时表。如果你仍然想在两者之间删除它们，那么你可以通过发出 \s5 命令来删除。
By default, all the temporary tables are deleted by MySQL when your database connection gets terminated. Still if you want to delete them in between, then you do so by issuing the DROP TABLE command.
以下程序是一个删除临时表的示例：
The following program is an example on dropping a temporary table −
mysql> CREATE TEMPORARY TABLE SalesSummary (
-> product_name VARCHAR(50) NOT NULL
-> , total_sales DECIMAL(12,2) NOT NULL DEFAULT 0.00
-> , avg_unit_price DECIMAL(7,2) NOT NULL DEFAULT 0.00
-> , total_units_sold INT UNSIGNED NOT NULL DEFAULT 0
);
Query OK, 0 rows affected (0.00 sec)
mysql> INSERT INTO SalesSummary
-> (product_name, total_sales, avg_unit_price, total_units_sold)
-> VALUES
-> ('cucumber', 100.25, 90, 2);
mysql> SELECT * FROM SalesSummary;
+--------------+-------------+----------------+------------------+
| product_name | total_sales | avg_unit_price | total_units_sold |
+--------------+-------------+----------------+------------------+
| cucumber | 100.25 | 90.00 | 2 |
+--------------+-------------+----------------+------------------+
1 row in set (0.00 sec)
mysql> DROP TABLE SalesSummary;
mysql> SELECT * FROM SalesSummary;
ERROR 1146: Table 'TUTORIALS.SalesSummary' doesn't existMySQL - Clone Tables
在某些情况下，你可能需要一张表的完全副本，并且 \s6 不符合你的目的，因为副本必须包含相同的索引、默认值等等。
There may be a situation when you need an exact copy of a table and CREATE TABLE … SELECT doesn’t suit your purposes because the copy must include the same indexes, default values and so forth.
通过以下步骤处理此情况：
You can handle this situation by following the steps given below −
-
Use SHOW CREATE TABLE to get a CREATE TABLE statement that specifies the source table’s structure, indexes and all.
-
Modify the statement to change the table name to that of the clone table and execute the statement. This way, you will have the exact clone table.
-
Optionally, if you need the table contents copied as well, issue an INSERT INTO … SELECT statement, too.
Example
尝试以下示例为 \s7 创建一个克隆表。
Try out the following example to create a clone table for tutorials_tbl.
Step 1 − 获取表中所有结构。
Step 1 − Get the complete structure about the table.
mysql> SHOW CREATE TABLE tutorials_tbl \G;
*************************** 1. row ***************************
Table: tutorials_tbl
Create Table: CREATE TABLE `tutorials_tbl` (
`tutorial_id` int(11) NOT NULL auto_increment,
`tutorial_title` varchar(100) NOT NULL default '',
`tutorial_author` varchar(40) NOT NULL default '',
`submission_date` date default NULL,
PRIMARY KEY (`tutorial_id`),
UNIQUE KEY `AUTHOR_INDEX` (`tutorial_author`)
) TYPE = MyISAM
1 row in set (0.00 sec)
ERROR:
No query specifiedStep 2 − 重命名此表并创建另一个表。
Step 2 − Rename this table and create another table.
mysql> CREATE TABLE clone_tbl (
-> tutorial_id int(11) NOT NULL auto_increment,
-> tutorial_title varchar(100) NOT NULL default '',
-> tutorial_author varchar(40) NOT NULL default '',
-> submission_date date default NULL,
-> PRIMARY KEY (tutorial_id),
-> UNIQUE KEY AUTHOR_INDEX (tutorial_author)
-> ) TYPE = MyISAM;
Query OK, 0 rows affected (1.80 sec)\s8 - 在执行步骤 2 后，你将在数据库中创建一个克隆表。如果你想从旧表中复制数据，那么你可以使用 INSERT INTO… SELECT 语句。
Step 3 − After executing step 2, you will create a clone table in your database. If you want to copy data from old table then you can do it by using INSERT INTO… SELECT statement.
mysql> INSERT INTO clone_tbl (tutorial_id,
-> tutorial_title,
-> tutorial_author,
-> submission_date)
-> SELECT tutorial_id,tutorial_title,
-> tutorial_author,submission_date
-> FROM tutorials_tbl;
Query OK, 3 rows affected (0.07 sec)
Records: 3 Duplicates: 0 Warnings: 0最后，您将拥有与您想要的一模一样的克隆表。
Finally, you will have an exact clone table as you wanted to have.
MySQL - Database Info
Obtaining and Using MySQL Metadata
有三种类型的信息你希望从 MySQL 获得。
There are three types of information, which you would like to have from MySQL.
-
Information about the result of queries − This includes the number of records affected by any SELECT, UPDATE or DELETE statement.
-
Information about the tables and databases − This includes information pertaining to the structure of the tables and the databases.
-
Information about the MySQL server − This includes the status of the database server, version number, etc.
在MySQL提示符下获取所有这些信息非常容易，但在使用PERL或PHP API时，我们需要显式调用各种API才能获取所有这些信息。
It is very easy to get all this information at the MySQL prompt, but while using PERL or PHP APIs, we need to call various APIs explicitly to obtain all this information.
Obtaining the Number of Rows Affected by a Query
现在让我们看看如何获取此信息。
Let is now see how to obtain this information.
PERL Example
在 DBI 脚本中，受影响的行数由 do( ) 或 execute( ) 命令返回，具体取决于如何执行查询。
In DBI scripts, the affected row count is returned by the do( ) or by the execute( ) command, depending on how you execute the query.
# Method 1
# execute $query using do( )
my $count = $dbh->do ($query);
# report 0 rows if an error occurred
printf "%d rows were affected\n", (defined ($count) ? $count : 0);
# Method 2
# execute query using prepare( ) plus execute( )
my $sth = $dbh->prepare ($query);
my $count = $sth->execute ( );
printf "%d rows were affected\n", (defined ($count) ? $count : 0);PHP Example
在 PHP 中，调用 mysql_affected_rows( ) 函数来找出查询更改了多少行。
In PHP, invoke the mysql_affected_rows( ) function to find out how many rows a query changed.
$result_id = mysql_query ($query, $conn_id);
# report 0 rows if the query failed
$count = ($result_id ? mysql_affected_rows ($conn_id) : 0);
print ("$count rows were affected\n");Listing Tables and Databases
列出所有数据库以及数据库服务器可用的表非常容易。如果你没有足够的权限，你的结果可能是 null 。
It is very easy to list down all the databases and the tables available with a database server. Your result may be null if you don’t have the sufficient privileges.
除了在以下代码块中显示的方法外，你还可以使用 SHOW TABLES 或 SHOW DATABASES 查询以在 PHP 或 PERL 中获取表或数据库列表。
Apart from the method which is shown in the following code block, you can use SHOW TABLES or SHOW DATABASES queries to get the list of tables or databases either in PHP or in PERL.
Using MySQL Sequences
序列是一组整数 1、2、3、…，它们是根据特定需求按顺序生成的。序列经常在数据库中使用，因为许多应用程序要求表中的每一行都包含一个唯一值，并且序列提供了一种简单的方法来生成它们。
A sequence is a set of integers 1, 2, 3, … that are generated in order on a specific demand. Sequences are frequently used in the databases because many applications require each row in a table to contain a unique value and sequences provide an easy way to generate them.
本章介绍如何在 MySQL 中使用序列。
This chapter describes how to use sequences in MySQL.
Using AUTO_INCREMENT Column
在 MySQL 中使用序列的最简单方法是将一列定义为 \s10，并将剩下的事情留给 MySQL 处理。
The simplest way in MySQL to use Sequences is to define a column as AUTO_INCREMENT and leave the remaining things to MySQL to take care.
Example
尝试以下示例。这将创建表，然后在其中插入几行，不需要提供记录 ID，因为 MySQL 会自动递增。
Try out the following example. This will create table and after that it will insert few rows in this table where it is not required to give record ID because it is auto incremented by MySQL.
mysql> CREATE TABLE insect
-> (
-> id INT UNSIGNED NOT NULL AUTO_INCREMENT,
-> PRIMARY KEY (id),
-> name VARCHAR(30) NOT NULL, # type of insect
-> date DATE NOT NULL, # date collected
-> origin VARCHAR(30) NOT NULL # where collected
);
Query OK, 0 rows affected (0.02 sec)
mysql> INSERT INTO insect (id,name,date,origin) VALUES
-> (NULL,'housefly','2001-09-10','kitchen'),
-> (NULL,'millipede','2001-09-10','driveway'),
-> (NULL,'grasshopper','2001-09-10','front yard');
Query OK, 3 rows affected (0.02 sec)
Records: 3 Duplicates: 0 Warnings: 0
mysql> SELECT * FROM insect ORDER BY id;
+----+-------------+------------+------------+
| id | name | date | origin |
+----+-------------+------------+------------+
| 1 | housefly | 2001-09-10 | kitchen |
| 2 | millipede | 2001-09-10 | driveway |
| 3 | grasshopper | 2001-09-10 | front yard |
+----+-------------+------------+------------+
3 rows in set (0.00 sec)Obtain AUTO_INCREMENT Values
LAST_INSERT_ID( ) 是一个 SQL 函数，因此，你可以从理解如何发出 SQL 语句的任何客户端内部使用它。否则，PERL 和 PHP 脚本提供独占函数来检索最后一条记录的自动增量值。
The LAST_INSERT_ID( ) is a SQL function, so you can use it from within any client that understands how to issue SQL statements. Otherwise, PERL and PHP scripts provide exclusive functions to retrieve the auto incremented value of the last record.
PERL Example
使用 mysql_insertid 特性来获取查询生成的 AUTO_INCREMENT 值。可以通过数据库句柄或语句句柄访问此特性，具体取决于发出查询的方式。
Use the mysql_insertid attribute to obtain the AUTO_INCREMENT value generated by a query. This attribute is accessed through either a database handle or a statement handle, depending on how you issue the query.
以下示例通过数据库句柄引用它。
The following example references it through the database handle.
$dbh->do ("INSERT INTO insect (name,date,origin)
VALUES('moth','2001-09-14','windowsill')");
my $seq = $dbh->{mysql_insertid};PHP Example
发出生成 AUTO_INCREMENT 值的查询后，通过调用 mysql_insert_id( ) 命令来检索值。
After issuing a query that generates an AUTO_INCREMENT value, retrieve the value by calling the mysql_insert_id( ) command.
mysql_query ("INSERT INTO insect (name,date,origin)
VALUES('moth','2001-09-14','windowsill')", $conn_id);
$seq = mysql_insert_id ($conn_id);Renumbering an Existing Sequence
可能会有这样一种情况：你已从表中删除了多条记录，并且想要重新对所有记录进行排序。这可以通过一个简单的技巧来完成，但如果你的表与另一个表有联接，则应非常小心地进行此操作。
There may be a case when you have deleted many records from a table and you want to re-sequence all the records. This can be done by using a simple trick, but you should be very careful to do so if your table is having joins with the other table.
如果你确定自动增量列的重新排序是不可避免的，那么执行它的方法是从表中删除该列，然后再次添加该列。
If you determine that the resequencing of an AUTO_INCREMENT column is unavoidable, the way to do it is to drop the column from the table, then add it again.
以下示例显示了使用此技术如何重新编号表中的 id values 。
The following example shows how to renumber the id values in the table using this technique.
mysql> ALTER TABLE insect DROP id;
mysql> ALTER TABLE insect
-> ADD id INT UNSIGNED NOT NULL AUTO_INCREMENT FIRST,
-> ADD PRIMARY KEY (id);Starting a Sequence at a Particular Value
默认情况下，MySQL 将从 1 开始排序，但你也可以在创建表时指定其他任何数字。
By default, MySQL will start sequence from 1, but you can specify any other number as well at the time of the table creation.
以下程序是一个示例，它展示了 MySQL 如何从 100 开始排序。
The following program is an example which shows how MySQL will start the sequence from 100.
mysql> CREATE TABLE insect
-> (
-> id INT UNSIGNED NOT NULL AUTO_INCREMENT = 100,
-> PRIMARY KEY (id),
-> name VARCHAR(30) NOT NULL, # type of insect
-> date DATE NOT NULL, # date collected
-> origin VARCHAR(30) NOT NULL # where collected
);或者，你可以创建表，然后使用 ALTER TABLE 命令设置初始排序值。
Alternatively, you can create the table and then set the initial sequence value with the ALTER TABLE command.
mysql> ALTER TABLE t AUTO_INCREMENT = 100;MySQL - Handling Duplicates
通常，表或结果集有时会包含重复记录。大多数时候它是允许的，但有时需要停止重复记录。需要识别重复记录并将它们从表中删除。本章将描述如何防止表中出现重复记录以及如何删除已存在的重复记录。
Generally, tables or result sets sometimes contain duplicate records. Most of the times it is allowed but sometimes it is required to stop duplicate records. It is required to identify duplicate records and remove them from the table. This chapter will describe how to prevent the occurrence of duplicate records in a table and how to remove the already existing duplicate records.
Preventing Duplicates from Occurring in a Table
你可以在表中使用 PRIMARY KEY 或 UNIQUE 索引和合适的字段来停止重复记录。
You can use a PRIMARY KEY or a UNIQUE Index on a table with the appropriate fields to stop duplicate records.
让我们举一个例子 - 以下表不包含此类索引或主键，因此它将允许 first_name 和 last_name 的重复记录。
Let us take an example – The following table contains no such index or primary key, so it would allow duplicate records for first_name and last_name.
CREATE TABLE person_tbl (
first_name CHAR(20),
last_name CHAR(20),
sex CHAR(10)
);为了防止创建带有相同名字和姓氏值的多个记录，请向其定义中添加一个 PRIMARY KEY 。执行此操作时，还需要声明索引列为 NOT NULL ，因为 PRIMARY KEY 不允许 NULL 值 -
To prevent multiple records with the same first and last name values from being created in this table, add a PRIMARY KEY to its definition. When you do this, it is also necessary to declare the indexed columns to be NOT NULL, because a PRIMARY KEY does not allow NULL values −
CREATE TABLE person_tbl (
first_name CHAR(20) NOT NULL,
last_name CHAR(20) NOT NULL,
sex CHAR(10),
PRIMARY KEY (last_name, first_name)
);表中存在唯一索引通常会导致出现错误，如果你向表中插入一条记录，该记录会使索引所定义的列或列中的现有记录重复。
The presence of a unique index in a table normally causes an error to occur if you insert a record into the table that duplicates an existing record in the column or columns that define the index.
使用 INSERT IGNORE 命令而不是 INSERT 命令。如果一条记录不会使现有记录重复，则 MySQL 会像往常一样插入它。如果记录重复，则 IGNORE 关键字会告诉 MySQL 在不生成错误的情况下静默地丢弃它。
Use the INSERT IGNORE command rather than the INSERT command. If a record doesn’t duplicate an existing record, then MySQL inserts it as usual. If the record is a duplicate, then the IGNORE keyword tells MySQL to discard it silently without generating an error.
以下示例不会出错，同时它也不会插入重复记录。
The following example does not error out and at the same time it will not insert duplicate records as well.
mysql> INSERT IGNORE INTO person_tbl (last_name, first_name)
-> VALUES( 'Jay', 'Thomas');
Query OK, 1 row affected (0.00 sec)
mysql> INSERT IGNORE INTO person_tbl (last_name, first_name)
-> VALUES( 'Jay', 'Thomas');
Query OK, 0 rows affected (0.00 sec)使用 REPLACE 命令而不是 INSERT 命令。如果该记录是新的，则会像 INSERT 一样插入它。如果它是重复，则新记录会替换旧记录。
Use the REPLACE command rather than the INSERT command. If the record is new, it is inserted just as with INSERT. If it is a duplicate, the new record replaces the old one.
mysql> REPLACE INTO person_tbl (last_name, first_name)
-> VALUES( 'Ajay', 'Kumar');
Query OK, 1 row affected (0.00 sec)
mysql> REPLACE INTO person_tbl (last_name, first_name)
-> VALUES( 'Ajay', 'Kumar');
Query OK, 2 rows affected (0.00 sec)INSERT IGNORE 和 REPLACE 命令应根据你想要影响的重复处理行为来选择。INSERT IGNORE 命令会保留第一组重复记录并丢弃其余记录。REPLACE 命令会保留最后一组重复记录并删除所有较早的记录。
The INSERT IGNORE and REPLACE commands should be chosen as per the duplicate-handling behavior you want to effect. The INSERT IGNORE command keeps the first set of the duplicated records and discards the remaining. The REPLACE command keeps the last set of duplicates and erases out any earlier ones.
另一种强制唯一性的方法是向表中添加 UNIQUE 索引而不是 PRIMARY KEY。
Another way to enforce uniqueness is to add a UNIQUE index rather than a PRIMARY KEY to a table.
CREATE TABLE person_tbl (
first_name CHAR(20) NOT NULL,
last_name CHAR(20) NOT NULL,
sex CHAR(10)
UNIQUE (last_name, first_name)
);Counting and Identifying Duplicates
以下是计算表中带有 first_name 和 last_name 的重复记录的查询。
Following is the query to count duplicate records with first_name and last_name in a table.
mysql> SELECT COUNT(*) as repetitions, last_name, first_name
-> FROM person_tbl
-> GROUP BY last_name, first_name
-> HAVING repetitions > 1;此查询将返回 person_tbl 表中的所有重复记录列表。通常情况下，要识别重复值的集合，请按照以下步骤操作。
This query will return a list of all the duplicate records in the person_tbl table. In general, to identify sets of values that are duplicated, follow the steps given below.
-
Determine which columns contain the values that may be duplicated.
-
List those columns in the column selection list, along with the COUNT()*.
-
List the columns in the GROUP BY clause as well.
-
Add a HAVING clause that eliminates the unique values by requiring the group counts to be greater than one.
Eliminating Duplicates from a Query Result
您可以将 DISTINCT 命令与 SELECT 语句结合使用，以找出表中可用的唯一记录。
You can use the DISTINCT command along with the SELECT statement to find out unique records available in a table.
mysql> SELECT DISTINCT last_name, first_name
-> FROM person_tbl
-> ORDER BY last_name;DISTINCT 命令的备用方法是添加一个 GROUP BY 子句，其中指定正在选择的列。这将消除重复项并仅选择指定列中值的唯一组合。
An alternative to the DISTINCT command is to add a GROUP BY clause that names the columns you are selecting. This has the effect of removing duplicates and selecting only the unique combinations of values in the specified columns.
mysql> SELECT last_name, first_name
-> FROM person_tbl
-> GROUP BY (last_name, first_name);Removing Duplicates Using Table Replacement
如果表中存在重复记录且要从该表中删除所有重复记录，请按照以下步骤操作。
If you have duplicate records in a table and you want to remove all the duplicate records from that table, then follow the procedure given below.
mysql> CREATE TABLE tmp SELECT last_name, first_name, sex
-> FROM person_tbl;
-> GROUP BY (last_name, first_name);
mysql> DROP TABLE person_tbl;
mysql> ALTER TABLE tmp RENAME TO person_tbl;从表中删除重复记录的一个简单方法是向该表中添加索引或主键。即使此表已可用，也可以使用此技术删除重复记录，未来也可以保证安全。
An easy way of removing duplicate records from a table is to add an INDEX or a PRIMARY KEY to that table. Even if this table is already available, you can use this technique to remove the duplicate records and you will be safe in future as well.
mysql> ALTER IGNORE TABLE person_tbl
-> ADD PRIMARY KEY (last_name, first_name);MySQL - and SQL Injection
如果通过网页获取用户输入并将其插入 MySQL 数据库，则很可能对以下安全问题持开放态度： SQL Injection 。此部分将指导如何帮助防止这种情况发生，并帮助您保护脚本和 MySQL 语句。
If you take user input through a webpage and insert it into a MySQL database, there’s a chance that you have left yourself wide open for a security issue known as SQL Injection. This chapter will teach you how to help prevent this from happening and help you secure your scripts and MySQL statements.
SQL 注入通常在您要求用户提供姓名等输入时发生，而他们没有提供姓名但提供了一个 MySQL 语句，而您却不知不觉地在自己的数据库中运行了该语句。
The SQL Injection usually occurs when you ask a user for input, like their name and instead of a name they give you a MySQL statement that you will unknowingly run on your database.
切勿信任用户提供的数据，仅在验证后处理此数据；一项规则是通过模式匹配完成此操作。在以下示例中，用户名限制为字母数字字符加下划线，且长度在 8 至 20 个字符之间 - 根据需要修改这些规则。
Never trust the data provided by a user, process this data only after validation; as a rule, this is done by pattern matching. In the following example, the username is restricted to alphanumerical characters plus underscore and to a length between 8 and 20 characters – modify these rules as needed.
if (preg_match("/^\w{8,20}$/", $_GET['username'], $matches)) {
$result = mysql_query("SELECT * FROM users WHERE username = $matches[0]");
} else {
echo "username not accepted";
}为了说明此问题，请考虑以下摘录。
To demonstrate this problem, consider the following excerpt.
// supposed input
$name = "Qadir'; DELETE FROM users;";
mysql_query("SELECT * FROM users WHERE name = '{$name}'");此函数调用应从 users 表中检索记录，其中 name 列与用户指定的 name 相匹配。在正常情况下，$name 仅包含字母数字字符及可能空格。但此处，通过附加一个全新的查询至 $name ，对数据库的调用将变成一场灾难。注入的 DELETE 查询删除了 users 中的所有记录。
The function call is supposed to retrieve a record from the users table, where the name column matches the name specified by the user. Under normal circumstances, $name would only contain alphanumeric characters and perhaps spaces. But here, by appending an entirely new query to $name, the call to the database turns into a disaster. The injected DELETE query removes all the records from users.
值得庆幸的是，如果您使用 MySQL， mysql_query() 函数不允许在单一的函数调用中查询堆栈或执行多个查询。如果您尝试堆叠查询，则调用会失败。
Fortunately, if you use MySQL, the mysql_query() function does not permit query stacking or executing multiple queries in a single function call. If you try to stack queries, the call fails.
但是，其他 PHP 数据库扩展程序，例如 SQLite 和 PostgreSQL ，愉快地执行堆叠的查询，执行在一个字符串中提供的查询并创建严重的安全问题。
However, other PHP database extensions, such as SQLite and PostgreSQL, happily perform stacked queries, executing all the queries provided in one string and creating a serious security problem.
Preventing SQL Injection
您可以在 PERL 和 PHP 等脚本语言中巧妙地处理所有转义字符。PHP 的 MySQL 扩展提供了 mysql_real_escape_string() 函数来转义对 MySQL 来说特殊的输入字符。
You can handle all escape characters smartly in scripting languages like PERL and PHP. The MySQL extension for PHP provides the function mysql_real_escape_string() to escape input characters that are special to MySQL.
if (get_magic_quotes_gpc()) {
$name = stripslashes($name);
}
$name = mysql_real_escape_string($name);
mysql_query("SELECT * FROM users WHERE name = '{$name}'");The LIKE Quandary
要解决 LIKE 难题，自定义转义机制必须将用户提供的 % 和 _ 字符转换为文本。使用 addcslashes() ，它是一个允许您指定要转义的字符范围的函数。
To address the LIKE quandary, a custom escaping mechanism must convert user-supplied % and _ characters to literals. Use addcslashes(), a function that lets you specify a character range to escape.
$sub = addcslashes(mysql_real_escape_string("%something_"), "%_");
// $sub == \%something\_
mysql_query("SELECT * FROM messages WHERE subject LIKE '{$sub}%'");MySQL - Database Export
将表数据导出到文本文件的最简单方法是使用 SELECT…INTO OUTFILE 语句，该语句将查询结果直接导出到服务器主机上的文件。
The simplest way of exporting a table data into a text file is by using the SELECT…INTO OUTFILE statement that exports a query result directly into a file on the server host.
Exporting Data with the SELECT … INTO OUTFILE Statement
此语句的语法将常规 SELECT 命令与结尾的 INTO OUTFILE filename 组合在一起。默认输出格式与 LOAD DATA 命令的格式相同。因此，以下语句将 tutorials_tbl 表导出到 /tmp/tutorials.txt 中，后者是一个制表符分隔、行尾符终止的文件。
The syntax for this statement combines a regular SELECT command with INTO OUTFILE filename at the end. The default output format is the same as it is for the LOAD DATA command. So, the following statement exports the tutorials_tbl table into /tmp/tutorials.txt as a tab-delimited, linefeed-terminated file.
mysql> SELECT * FROM tutorials_tbl
-> INTO OUTFILE '/tmp/tutorials.txt';您可以使用各种选项更改输出格式，以指示如何引用和分隔列和记录。要使用 CRLF 终止行以 CSV 格式导出 tutorial_tbl 表，请使用以下代码。
You can change the output format using various options to indicate how to quote and delimit columns and records. To export the tutorial_tbl table in a CSV format with CRLF-terminated lines, use the following code.
mysql> SELECT * FROM passwd INTO OUTFILE '/tmp/tutorials.txt'
-> FIELDS TERMINATED BY ',' ENCLOSED BY '"'
-> LINES TERMINATED BY '\r\n';SELECT … INTO OUTFILE 具有以下属性：
The SELECT … INTO OUTFILE has the following properties −
-
The output file is created directly by the MySQL server, so the filename should indicate where you want the file to be written on the server host. There is no LOCAL version of the statement analogous to the LOCAL version of LOAD DATA.
-
You must have the MySQL FILE privilege to execute the SELECT … INTO statement.
-
The output file must not already exist. This prevents MySQL from clobbering files that may be important.
-
You should have a login account on the server host or some way to retrieve the file from that host. Otherwise, the SELECT … INTO OUTFILE command will most likely be of no value to you.
-
Under UNIX, the file is created world readable and is owned by the MySQL server. This means that although you will be able to read the file, you may not be able to delete it.
Exporting Tables as Raw Data
mysqldump 程序用于复制或备份表格和数据库。它可以将表格输出写入 Raw Datafile 或 INSERT 陈述集，在表格中重新创建记录。
The mysqldump program is used to copy or back up tables and databases. It can write the table output either as a Raw Datafile or as a set of INSERT statements that recreate the records in the table.
要将表格作为数据文件倾卸，您必须指定 --tab 选项，表示目录，您希望 MySQL 服务器在此目录中写入文件。
To dump a table as a datafile, you must specify a --tab option that indicates the directory, where you want the MySQL server to write the file.
例如，要将 TUTORIALS 数据库中的 tutorials_tbl 表格倾卸到 /tmp 目录的一个文件中，请使用如下所示的命令。
For example, to dump the tutorials_tbl table from the TUTORIALS database to a file in the /tmp directory, use a command as shown below.
$ mysqldump -u root -p --no-create-info \
--tab=/tmp tutorials tutorials_tbl
password ******Exporting Table Contents or Definitions in SQL Format
要以 SQL 格式将表格导出到文件中，请使用如下所示的命令。
To export a table in SQL format to a file, use the command shown below.
$ mysqldump -u root -p TUTORIALS tutorials_tbl > dump.txt
password ******此操作将创建一个包含如下所示内容的文件。
This will a create file having content as shown below.
-- MySQL dump 8.23
--
-- Host: localhost Database: TUTORIALS
---------------------------------------------------------
-- Server version 3.23.58
--
-- Table structure for table `tutorials_tbl`
--
CREATE TABLE tutorials_tbl (
tutorial_id int(11) NOT NULL auto_increment,
tutorial_title varchar(100) NOT NULL default '',
tutorial_author varchar(40) NOT NULL default '',
submission_date date default NULL,
PRIMARY KEY (tutorial_id),
UNIQUE KEY AUTHOR_INDEX (tutorial_author)
) TYPE = MyISAM;
--
-- Dumping data for table `tutorials_tbl`
--
INSERT INTO tutorials_tbl
VALUES (1,'Learn PHP','John Poul','2007-05-24');
INSERT INTO tutorials_tbl
VALUES (2,'Learn MySQL','Abdul S','2007-05-24');
INSERT INTO tutorials_tbl
VALUES (3,'JAVA Tutorial','Sanjay','2007-05-06');要倾卸多个表格，请为它们全部指定名称，后接数据库名称参数。要倾卸整个数据库，不要在数据库后面指定任何表格，如下面的代码块中所示。
To dump multiple tables, name them all followed by the database name argument. To dump an entire database, don’t name any tables after the database as shown in the following code block.
$ mysqldump -u root -p TUTORIALS > database_dump.txt
password ******要备份您的主机上提供的所有数据库，请使用以下代码。
To back up all the databases available on your host, use the following code.
$ mysqldump -u root -p --all-databases > database_dump.txt
password ******--all-databases 选项在 MySQL 3.23.12 版本中可用。这种方法可用于实现数据库备份策略。
The --all-databases option is available in the MySQL 3.23.12 version. This method can be used to implement a database backup strategy.
Copying Tables or Databases to Another Host
如果您想从一台 MySQL 服务器复制表格或数据库到另一台服务器，请使用 mysqldump 以及数据库名称和表格名称。
If you want to copy tables or databases from one MySQL server to another, then use the mysqldump with database name and table name.
在源主机上运行以下命令。这会将完整的数据库倾卸到 dump.txt 文件中。
Run the following command at the source host. This will dump the complete database into dump.txt file.
$ mysqldump -u root -p database_name table_name > dump.txt
password *****您可以如上所述在不使用特定表格名称的情况下复制完整的数据库。
You can copy complete database without using a particular table name as explained above.
现在，在另一台主机上 ftp dump.txt 文件，并使用以下命令。在运行此命令之前，确保在目标服务器上已创建 database_name。
Now, ftp dump.txt file on another host and use the following command. Before running this command, make sure you have created database_name on destination server.
$ mysql -u root -p database_name < dump.txt
password *****无需使用中间文件即可完成此操作的另一种方法是将 mysqldump 的输出直接通过网络发送到远程 MySQL 服务器。如果您能从源数据库所在的主机连接到两台服务器，请使用以下命令（确保您在两台服务器上都有权限）。
Another way to accomplish this without using an intermediary file is to send the output of the mysqldump directly over the network to the remote MySQL server. If you can connect to both the servers from the host where the source database resides, use the following command (Make sure you have access on both the servers).
$ mysqldump -u root -p database_name \
| mysql -h other-host.com database_name在 mysqldump 中，一半命令连接到本地服务器并将倾卸输出写入管道。命令的另一半连接到 other-host.com 上的远程 MySQL 服务器。它读取管道的输入并将每个语句发送到 other-host.com 服务器。
In mysqldump, half of the command connects to the local server and writes the dump output to the pipe. The remaining half of the command connects to the remote MySQL server on the other-host.com. It reads the pipe for input and sends each statement to the other-host.com server.
MySQL - Database Import - Recovery Methods
在 MySQL 中有两种简单的方法可以从先前备份的文件中将数据加载到 MySQL 数据库中。
There are two simple ways in MySQL to load data into the MySQL database from a previously backed up file.
Importing Data with LOAD DATA
MySQL提供了一个LOAD DATA语句，用作批量数据加载程序。以下是一个示例语句，它从当前目录中读取文件 dump.txt 并将该文件加载到当前数据库中的表 mytbl 中。
MySQL provides a LOAD DATA statement that acts as a bulk data loader. Here is an example statement that reads a file dump.txt from your current directory and loads it into the table mytbl in the current database.
mysql> LOAD DATA LOCAL INFILE 'dump.txt' INTO TABLE mytbl;-
If the LOCAL keyword is not present, MySQL looks for the datafile on the server host using the looking into absolute pathname, which fully specifies the location of the file, beginning from the root of the filesystem. MySQL reads the file from the given location.
-
By default, LOAD DATA assumes that datafiles contain lines that are terminated by linefeeds (newlines) and that data values within a line are separated by tabs.
-
To specify a file format explicitly, use a FIELDS clause to describe the characteristics of fields within a line, and a LINES clause to specify the line-ending sequence. The following LOAD DATA statement specifies that the datafile contains values separated by colons and lines terminated by carriage returns and new line character.
mysql> LOAD DATA LOCAL INFILE 'dump.txt' INTO TABLE mytbl
-> FIELDS TERMINATED BY ':'
-> LINES TERMINATED BY '\r\n';-
The LOAD DATA command assumes the columns in the datafile have the same order as the columns in the table. If that is not true, you can specify a list to indicate which table columns the datafile columns should be loaded into. Suppose your table has columns a, b, and c, but successive columns in the datafile correspond to columns b, c, and a.
您可以如以下代码块所示加载文件。
You can load the file as shown in the following code block.
mysql> LOAD DATA LOCAL INFILE 'dump.txt'
-> INTO TABLE mytbl (b, c, a);Importing Data with mysqlimport
MySQL还包括一个名为 mysqlimport 的实用程序，它充当LOAD DATA的包装，以便您可以直接从命令行加载输入文件。
MySQL also includes a utility program named mysqlimport that acts as a wrapper around LOAD DATA, so that you can load the input files directly from the command line.
要从 dump.txt 将数据加载到 mytbl ，请在UNIX提示符下使用以下命令。
To load data from the dump.txt into mytbl, use the following command at the UNIX prompt.
$ mysqlimport -u root -p --local database_name dump.txt
password *****如果使用 mysqlimport ，则命令行选项提供格式说明符。与前两个 LOAD DATA 语句相对应的 mysqlimport 命令如下所示代码块所示。
If you use mysqlimport, command-line options provide the format specifiers. The mysqlimport commands that correspond to the preceding two LOAD DATA statements looks as shown in the following code block.
$ mysqlimport -u root -p --local --fields-terminated-by = ":" \
--lines-terminated-by = "\r\n" database_name dump.txt
password *****对于mysqlimport来说，指定选项的顺序并不重要，但它们都应在数据库名称之前。
The order in which you specify the options doesn’t matter for mysqlimport, except that they should all precede the database name.
mysqlimport 语句使用 --columns 选项来指定列顺序−
The mysqlimport statement uses the --columns option to specify the column order −
$ mysqlimport -u root -p --local --columns=b,c,a \
database_name dump.txt
password *****Handling Quotes and Special Characters
除了 TERMINATED BY 之外，FIELDS子句还可以指定其他格式选项。默认情况下，LOAD DATA假设值未加引号，并将反斜杠（\）解释为特殊字符的转义字符。若要显式指示值引号字符，请使用 ENCLOSED BY 命令。MySQL将在输入处理过程中从数据值的末端去除该字符。若要更改默认转义字符，请使用 ESCAPED BY 。
The FIELDS clause can specify other format options besides TERMINATED BY. By default, LOAD DATA assumes that values are unquoted and interprets the backslash (\) as an escape character for the special characters. To indicate the value quoting character explicitly, use the ENCLOSED BY command. MySQL will strip that character from the ends of data values during input processing. To change the default escape character, use ESCAPED BY.
当指定ENCLOSED BY以指示应从数据值中删除引号字符时，可以通过加倍或在之前加转义字符将引号字符作为数据值中的文字包括在内。
When you specify ENCLOSED BY to indicate that quote characters should be stripped from data values, it is possible to include the quote character literally within data values by doubling it or by preceding it with the escape character.
例如，如果引号和转义字符为“和\,则输入值 "a""b\"c" 将解释为 a"b"c 。
For example, if the quote and escape characters are " and \, the input value "a""b\"c" will be interpreted as a"b"c.
对于 mysqlimport ，用于指定引号和转义值的对应命令行选项为 --fields-enclosed-by 和 --fields-escaped-by 。
For mysqlimport, the corresponding command-line options for specifying quote and escape values are --fields-enclosed-by and --fields-escaped-by.