Mysqli 简明教程
MySQLi - Introduction
MySQLi 是 PHP 中 MySQL API 的一个扩展，从 PHP 5.0 开始使用。它也被称为改良的 MySQL 扩展。MySQLi 背后的动机是要利用 MySQL 4.1.3 及更高版本中可用新功能的优势。它提供了比 MySQL 扩展有许多优势。
MySQLi is an extension to MySQL API available in PHP and is introduced from PHP 5.0 onwards. It is also known as MySQL improved extension. Motivation behind MySQLi was to take advantage of new features available in MySQL 4.1.3 onwards. It provides numerous benefits over MySQL extension.
-
MySQL provides an object oriented interface. It provides both object oriented and procedural approach to handle database operations.
Object Oriented Interface
<?php
$mysqli = mysqli_connect("localhost", "user", "password", "database-name");
$result = mysqli_query($mysqli, "SELECT 'Welcome to MySQLi' AS _msg FROM DUAL");
$row = mysqli_fetch_assoc($result);
echo $row['_msg'];
?>Procedural Approach
<?php
$mysqli = new mysqli("localhost", "user", "password", "database-name");
$result = $mysqli→query("SELECT 'Welcome to MySQLi' AS _msg FROM DUAL");
$row = $result→fetch_assoc();
echo $row['_msg'];
?>-
MySQLi supports prepared statments.
-
MySQLi supports multiple statments.
-
MySQLi supports transactions.
-
MySQLi provides enhanced debugging capabilities.
MySQLi - 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 −
mysqli 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 −
$mysqli = new mysqli($dbhost, $dbuser, $dbpass, $dbname);
mysqli→query(,"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
$retval = mysqli - > <i>function</i>(value, [value,...]);
if( !$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.
MySQLi - 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:******这会给你 MySQL 命令提示符，你可以在其中执行任何 SQL 命令。以下是上述命令的结果−
This will give you the mysqli 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 mysqli 构造或 mysqli_connect() 函数来打开一个数据库连接。此函数采用六个参数，并且在成功时返回一个 MySQL 链接标识符，在失败时返回 FALSE。
PHP provides mysqli contruct or mysqli_connect() function to open a database connection. This function takes six parameters and returns a MySQL link identifier on success or FALSE on failure.
Syntax
$mysqli = new mysqli($host, $username, $passwd, $dbName, $port, $socket);Sr.No. |
Parameter & Description |
1 |
$host Optional − The host name running the database server. If not specified, then the default value will be localhost:3306. |
2 |
$username Optional − The username accessing the database. If not specified, then the default will be the name of the user that owns the server process. |
3 |
$passwd Optional − The password of the user accessing the database. If not specified, then the default will be an empty password. |
4 |
$dbName Optional − database name on which query is to be performed. |
5 |
$port Optional − the port number to attempt to connect to the MySQL server.. |
6 |
$socket Optional − socket or named pipe that should be used. |
你可以随时使用另一个 PHP 函数 close() 来断开 MySQL 数据库连接。
You can disconnect from the MySQL database anytime using another PHP function close().
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 −
将以下示例复制粘贴为 mysql_example.php：
Copy and paste the following example as mysql_example.php −
<html>
<head>
<title>Connecting MySQL Server</title>
</head>
<body>
<?php
$dbhost = 'localhost';
$dbuser = 'root';
$dbpass = 'root@123';
$mysqli = new mysqli($dbhost, $dbuser, $dbpass);
if($mysqli→connect_errno ) {
printf("Connect failed: %s<br />", $mysqli→connect_error);
exit();
}
printf('Connected successfully.<br />');
$mysqli→close();
?>
</body>
</html>MySQLi - 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 mysqli query() 或 mysql_query() 函数来创建或删除 MySQL 数据库。这个函数接收两个参数，并在成功时返回 TRUE，并在失败时返回 FALSE。
PHP uses mysqli query() or mysql_query() function to create or delete a MySQL database. This function takes two parameters and returns TRUE on success or FALSE on failure.
Syntax
$mysqli→query($sql,$resultmode)Sr.No. |
Parameter & Description |
1 |
$sql Required - SQL query to create a MySQL database. |
2 |
$resultmode Optional - Either the constant MYSQLI_USE_RESULT or MYSQLI_STORE_RESULT depending on the desired behavior. By default, MYSQLI_STORE_RESULT is used. |
Example
尝试以下示例来创建数据库 −
Try the following example to create a database −
将以下示例复制粘贴为 mysql_example.php：
Copy and paste the following example as mysql_example.php −
<html>
<head><title>Creating MySQL Database</title></head>
<body>
<?php
$dbhost = 'localhost';
$dbuser = 'root';
$dbpass = 'root@123';
$mysqli = new mysqli($dbhost, $dbuser, $dbpass);
if($mysqli→connect_errno ) {
printf("Connect failed: %s<br />", $mysqli→connect_error);
exit();
}
printf('Connected successfully.<br />');
if ($mysqli→query("CREATE DATABASE TUTORIALS")) {
printf("Database TUTORIALS created successfully.<br />");
}
if ($mysqli→errno) {
printf("Could not create database: %s<br />", $mysqli→error);
}
$mysqli→close();
?>
</body>
</html>MySQLi - Drop 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 mysqli query() 或 mysql_query() 函数来删除 MySQL 数据库。这个函数接收两个参数，并在成功时返回 TRUE，并在失败时返回 FALSE。
PHP uses mysqli query() or mysql_query() function to drop a MySQL database. This function takes two parameters and returns TRUE on success or FALSE on failure.
Syntax
$mysqli→query($sql,$resultmode)Sr.No. |
Parameter & Description |
1 |
$sql Required - SQL query to drop a MySQL database. |
2 |
$resultmode Optional - Either the constant MYSQLI_USE_RESULT or MYSQLI_STORE_RESULT depending on the desired behavior. By default, MYSQLI_STORE_RESULT is used. |
Example
尝试以下示例来删除数据库−
Try the following example to drop a database −
将以下示例复制粘贴为 mysql_example.php：
Copy and paste the following example as mysql_example.php −
<html>
<head><title>Dropping MySQL Database</title></head>
<body>
<?php
$dbhost = 'localhost';
$dbuser = 'root';
$dbpass = 'root@123';
$mysqli = new mysqli($dbhost, $dbuser, $dbpass);
if($mysqli->connect_errno ) {
printf("Connect failed: %s<br />", $mysqli->connect_error);
exit();
}
printf('Connected successfully.<br />');
if ($mysqli->query("Drop DATABASE TUTORIALS")) {
printf("Database TUTORIALS dropped successfully.<br />");
}
if ($mysqli->errno) {
printf("Could not drop database: %s<br />", $mysqli->error);
}
$mysqli->close();
?>
</body>
</html>MySQLi - Select 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 使用 mysqli_select_db 函数来选择要执行查询的数据库。此函数接受两个参数，并成功时返回 TRUE，失败时返回 FALSE。
PHP uses mysqli_select_db function to select the database on which queries are to be performed. This function takes two parameters and returns TRUE on success or FALSE on failure.
Syntax
mysqli_select_db ( mysqli $link , string $dbname ) : boolSr.No. |
Parameter & Description |
1 |
$link Required - A link identifier returned by mysqli_connect() or mysqli_init(). |
2 |
$dbname Required - Name of the database to be connected. |
Example
尝试以下示例以选择数据库 −
Try the following example to select a database −
将以下示例复制粘贴为 mysql_example.php：
Copy and paste the following example as mysql_example.php −
<html>
<head>
<title>Selecting MySQL Database</title>
</head>
<body>
<?php
$dbhost = 'localhost';
$dbuser = 'root';
$dbpass = 'root@123';
$conn = mysqli_connect($dbhost, $dbuser, $dbpass);
if(! $conn ) {
die('Could not connect: ' . mysqli_error($conn));
}
echo 'Connected successfully<br />';
$retval = mysqli_select_db( $conn, 'TUTORIALS' );
if(! $retval ) {
die('Could not select database: ' . mysqli_error($conn));
}
echo "Database TUTORIALS selected successfully\n";
mysqli_close($conn);
?>
</body>
</html>MySQLi - Create Table
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
PHP 使用 mysqli query() 或 mysql_query() 函数来创建 MySQL 表。这个函数接收两个参数，并在成功时返回 TRUE，并在失败时返回 FALSE。
PHP uses mysqli query() or mysql_query() function to create a MySQL table. This function takes two parameters and returns TRUE on success or FALSE on failure.
Syntax
$mysqli→query($sql,$resultmode)Sr.No. |
Parameter & Description |
1 |
$sql Required - SQL query to create a MySQL table. |
2 |
$resultmode Optional - Either the constant MYSQLI_USE_RESULT or MYSQLI_STORE_RESULT depending on the desired behavior. By default, MYSQLI_STORE_RESULT is used. |
Example
尝试以下示例以创建一个表 −
Try the following example to create a table −
将以下示例复制粘贴为 mysql_example.php：
Copy and paste the following example as mysql_example.php −
<html>
<head>
<title>Creating MySQL Table</title>
</head>
<body>
<?php
$dbhost = 'localhost';
$dbuser = 'root';
$dbpass = 'root@123';
$dbname = 'TUTORIALS';
$mysqli = new mysqli($dbhost, $dbuser, $dbpass, $dbname);
if($mysqli→connect_errno ) {
printf("Connect failed: %s<br />", $mysqli→connect_error);
exit();
}
printf('Connected successfully.<br />');
$sql = "CREATE TABLE tutorials_tbl( ".
"tutorial_id INT NOT NULL AUTO_INCREMENT, ".
"tutorial_title VARCHAR(100) NOT NULL, ".
"tutorial_author VARCHAR(40) NOT NULL, ".
"submission_date DATE, ".
"PRIMARY KEY ( tutorial_id )); ";
if ($mysqli→query($sql)) {
printf("Table tutorials_tbl created successfully.<br />");
}
if ($mysqli→errno) {
printf("Could not create table: %s<br />", $mysqli→error);
}
$mysqli→close();
?>
</body>
</html>MySQLi - Drop Table
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
PHP 使用 mysqli query() 或 mysql_query() 函数来删除 MySQL 表。这个函数接收两个参数，并在成功时返回 TRUE，并在失败时返回 FALSE。
PHP uses mysqli query() or mysql_query() function to drop a MySQL table. This function takes two parameters and returns TRUE on success or FALSE on failure.
Syntax
$mysqli→query($sql,$resultmode)Sr.No. |
Parameter & Description |
1 |
$sql Required - SQL query to drop a table. |
2 |
$resultmode Optional - Either the constant MYSQLI_USE_RESULT or MYSQLI_STORE_RESULT depending on the desired behavior. By default, MYSQLI_STORE_RESULT is used. |
Example
尝试以下示例来删除一个表格 −
Try the following example to drop a table −
将以下示例复制粘贴为 mysql_example.php：
Copy and paste the following example as mysql_example.php −
<html>
<head>
<title>Dropping MySQL Table</title>
</head>
<body>
<?php
$dbhost = 'localhost';
$dbuser = 'root';
$dbpass = 'root@123';
$dbname = 'TUTORIALS';
$mysqli = new mysqli($dbhost, $dbuser, $dbpass, $dbname);
if($mysqli→connect_errno ) {
printf("Connect failed: %s<br />", $mysqli→connect_error);
exit();
}
printf('Connected successfully.<br />');
if ($mysqli→query("Drop Table tutorials_tbl")) {
printf("Table tutorials_tbl dropped successfully.<br />");
}
if ($mysqli→errno) {
printf("Could not drop table: %s<br />", $mysqli→error);
}
$mysqli→close();
?>
</body>
</html>MySQLi - 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
PHP 使用 mysqli query() 或 mysql_query() 函数向 MySQL 表中插入记录。此函数接受两个参数，在成功时返回 TRUE，在失败时返回 FALSE。
PHP uses mysqli query() or mysql_query() function to insert a record into a MySQL table. This function takes two parameters and returns TRUE on success or FALSE on failure.
Syntax
$mysqli→query($sql,$resultmode)Sr.No. |
Parameter & Description |
1 |
$sql Required - SQL query to insert record into a table. |
2 |
$resultmode Optional - Either the constant MYSQLI_USE_RESULT or MYSQLI_STORE_RESULT depending on the desired behavior. By default, MYSQLI_STORE_RESULT is used. |
Example
此示例将从用户那里获取三个参数，并将它们插入 MySQL 表 − −
This example will take three parameters from the user and will insert them into the MySQL table − −
将以下示例复制粘贴为 mysql_example.php：
Copy and paste the following example as mysql_example.php −
<html>
<head>
<title>Add New Record in MySQL Database</title>
</head>
<body>
<?php
if(isset($_POST['add'])) {
$dbhost = 'localhost';
$dbuser = 'root';
$dbpass = 'root@123';
$dbname = 'TUTORIALS';
$mysqli = new mysqli($dbhost, $dbuser, $dbpass, $dbname);
if($mysqli→connect_errno ) {
printf("Connect failed: %s<br />", $mysqli→connect_error);
exit();
}
printf('Connected successfully.<br />');
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')";
if ($mysqli→query($sql)) {
printf("Record inserted successfully.<br />");
}
if ($mysqli→errno) {
printf("Could not insert record into table: %s<br />", $mysqli→error);
}
$mysqli→close();
} 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>Output
访问部署在 apache Web 服务器上的 mysql_example.php，输入详细信息，并在提交表单时验证输出。
Access the mysql_example.php deployed on apache web server, enter details and verify the output on submitting the form.
Record inserted successfully.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.
MySQLi - 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
PHP 使用 mysqli query() 或 mysql_query() 函数来从 MySQL 表中选择记录。这个函数接收两个参数，并在成功时返回 TRUE，并在失败时返回 FALSE。
PHP uses mysqli query() or mysql_query() function to select records from a MySQL table. This function takes two parameters and returns TRUE on success or FALSE on failure.
Syntax
$mysqli→query($sql,$resultmode)Sr.No. |
Parameter & Description |
1 |
$sql Required - SQL query to select records from a MySQL table. |
2 |
$resultmode Optional - Either the constant MYSQLI_USE_RESULT or MYSQLI_STORE_RESULT depending on the desired behavior. By default, MYSQLI_STORE_RESULT is used. |
Example
尝试使用以下示例从表中选择记录-
Try the following example to select a record from a table −
将以下示例复制粘贴为 mysql_example.php：
Copy and paste the following example as mysql_example.php −
<html>
<head>
<title>Creating MySQL Table</title>
</head>
<body>
<?php
$dbhost = 'localhost';
$dbuser = 'root';
$dbpass = 'root@123';
$dbname = 'TUTORIALS';
$mysqli = new mysqli($dbhost, $dbuser, $dbpass, $dbname);
if($mysqli→connect_errno ) {
printf("Connect failed: %s<br />", $mysqli→connect_error);
exit();
}
printf('Connected successfully.<br />');
$sql = "SELECT tutorial_id, tutorial_title, tutorial_author, submission_date FROM tutorials_tbl";
$result = $mysqli->query($sql);
if ($result->num_rows > 0) {
while($row = $result->fetch_assoc()) {
printf("Id: %s, Title: %s, Author: %s, Date: %d <br />",
$row["tutorial_id"],
$row["tutorial_title"],
$row["tutorial_author"],
$row["submission_date"]);
}
} else {
printf('No record found.<br />');
}
mysqli_free_result($result);
$mysqli→close();
?>
</body>
</html>Output
访问在 apache web 服务器上部署的 mysql_example.php，并验证输出。在运行选择脚本之前，我们在此表中输入了多条记录。
Access the mysql_example.php deployed on apache web server and verify the output. Here we’ve entered multiple records in the table before running the select script.
Connected successfully.
Id: 1, Title: MySQL Tutorial, Author: Mahesh, Date: 2021
Id: 2, Title: HTML Tutorial, Author: Mahesh, Date: 2021
Id: 3, Title: PHP Tutorial, Author: Mahesh, Date: 2021
Id: 4, Title: Java Tutorial, Author: Mahesh, Date: 2021
Id: 5, Title: Apache Tutorial, Author: Suresh, Date: 2021MySQLi - 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 −
Operator |
Description |
Example |
= |
Checks if the values of the two operands are equal or not, if yes, then the condition becomes true. |
(A = B) is not true. |
!= |
Checks if the values of the two operands are equal or not, if the values are not equal then the condition becomes true. |
(A != B) is true. |
> |
Checks if the value of the left operand is greater than the value of the right operand, if yes, then the condition becomes true. |
(A > B) is not true. |
< |
Checks if the value of the left operand is less than the value of the right operand, if yes then the condition becomes true. |
(A < B) is true. |
>= |
Checks if the value of the left operand is greater than or equal to the value of the right operand, if yes, then the condition becomes true. |
(A >= B) is not true. |
⇐ |
Checks if the value of the left operand is less than or equal to the value of the right operand, if yes, then the condition becomes true. |
(A ⇐ B) is true. |
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
PHP 使用 mysqli query() 或 mysql_query() 函数通过 where 子句选择 MySQL 表中的记录。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 mysqli query() or mysql_query() function to select records in a MySQL table using where clause. This function takes two parameters and returns TRUE on success or FALSE on failure.
Syntax
$mysqli→query($sql,$resultmode)Sr.No. |
Parameter & Description |
1 |
$sql Required - SQL query to select records in a MySQL table using Where Clause. |
2 |
$resultmode Optional - Either the constant MYSQLI_USE_RESULT or MYSQLI_STORE_RESULT depending on the desired behavior. By default, MYSQLI_STORE_RESULT is used. |
Example
尝试以下示例，通过表中的 where 子句选择记录 −
Try the following example to select a record using where clause in a table −
将以下示例复制粘贴为 mysql_example.php：
Copy and paste the following example as mysql_example.php −
<html>
<head>
<title>Using Where Clause</title>
</head>
<body>
<?php
$dbhost = 'localhost';
$dbuser = 'root';
$dbpass = 'root@123';
$dbname = 'TUTORIALS';
$mysqli = new mysqli($dbhost, $dbuser, $dbpass, $dbname);
if($mysqli→connect_errno ) {
printf("Connect failed: %s<br />", $mysqli→connect_error);
exit();
}
printf('Connected successfully.<br />');
$sql = 'SELECT tutorial_id, tutorial_title, tutorial_author, submission_date FROM tutorials_tbl where tutorial_author = "Mahesh"';
$result = $mysqli→query($sql);
if ($result→num_rows > 0) {
while($row = $result→fetch_assoc()) {
printf("Id: %s, Title: %s, Author: %s, Date: %d <br />",
$row["tutorial_id"],
$row["tutorial_title"],
$row["tutorial_author"],
$row["submission_date"]);
}
} else {
printf('No record found.<br />');
}
mysqli_free_result($result);
$mysqli→close();
?>
</body>
</html>Output
访问在 apache web 服务器上部署的 mysql_example.php，并验证输出。在运行选择脚本之前，我们在此表中输入了多条记录。
Access the mysql_example.php deployed on apache web server and verify the output. Here we’ve entered multiple records in the table before running the select script.
Connected successfully.
Id: 1, Title: MySQL Tutorial, Author: Mahesh, Date: 2021
Id: 2, Title: HTML Tutorial, Author: Mahesh, Date: 2021
Id: 3, Title: PHP Tutorial, Author: Mahesh, Date: 2021MySQLi - 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
PHP 使用 mysqli query() 或 mysql_query() 函数来更新 MySQL 表中的记录。此函数接收两个参数，成功时返回 TRUE，失败时返回 FALSE。
PHP uses mysqli query() or mysql_query() function to update records in a MySQL table. This function takes two parameters and returns TRUE on success or FALSE on failure.
Syntax
$mysqli→query($sql,$resultmode)Sr.No. |
Parameter & Description |
1 |
$sql Required - SQL query to update records in a MySQL table. |
2 |
$resultmode Optional - Either the constant MYSQLI_USE_RESULT or MYSQLI_STORE_RESULT depending on the desired behavior. By default, MYSQLI_STORE_RESULT is used. |
Example
尝试使用以下示例来更新表中的记录-
Try the following example to update a record in a table −
将以下示例复制粘贴为 mysql_example.php：
Copy and paste the following example as mysql_example.php −
<html>
<head>
<title>Updating MySQL Table</title>
</head>
<body>
<?php
$dbhost = 'localhost';
$dbuser = 'root';
$dbpass = 'root@123';
$dbname = 'TUTORIALS';
$mysqli = new mysqli($dbhost, $dbuser, $dbpass, $dbname);
if($mysqli→connect_errno ) {
printf("Connect failed: %s<br />", $mysqli→connect_error);
exit();
}
printf('Connected successfully.<br />');
if ($mysqli→query('UPDATE tutorials_tbl set tutorial_title = "Learning Java" where tutorial_id = 4')) {
printf("Table tutorials_tbl updated successfully.<br />");
}
if ($mysqli→errno) {
printf("Could not update table: %s<br />", $mysqli→error);
}
$sql = "SELECT tutorial_id, tutorial_title, tutorial_author, submission_date FROM tutorials_tbl";
$result = $mysqli→query($sql);
if ($result→num_rows > 0) {
while($row = $result→fetch_assoc()) {
printf("Id: %s, Title: %s, Author: %s, Date: %d <br />",
$row["tutorial_id"],
$row["tutorial_title"],
$row["tutorial_author"],
$row["submission_date"]);
}
} else {
printf('No record found.<br />');
}
mysqli_free_result($result);
$mysqli→close();
?>
</body>
</html>Output
访问在 apache web 服务器上部署的 mysql_example.php，并验证输出。在运行选择脚本之前，我们在此表中输入了多条记录。
Access the mysql_example.php deployed on apache web server and verify the output. Here we’ve entered multiple records in the table before running the select script.
Connected successfully.
Table tutorials_tbl updated successfully.
Id: 1, Title: MySQL Tutorial, Author: Mahesh, Date: 2021
Id: 2, Title: HTML Tutorial, Author: Mahesh, Date: 2021
Id: 3, Title: PHP Tutorial, Author: Mahesh, Date: 2021
Id: 4, Title: Learning Java, Author: Mahesh, Date: 2021
Id: 5, Title: Apache Tutorial, Author: Suresh, Date: 2021MySQLi - 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
PHP 使用 mysqli query() 或 mysql_query() 函数来删除 MySQL 表中的记录。这个函数接收两个参数，并在成功时返回 TRUE，并在失败时返回 FALSE。
PHP uses mysqli query() or mysql_query() function to delete records in a MySQL table. This function takes two parameters and returns TRUE on success or FALSE on failure.
Syntax
$mysqli→query($sql,$resultmode)Sr.No. |
Parameter & Description |
1 |
$sql Required - SQL query to delete records in a MySQL table. |
2 |
$resultmode Optional - Either the constant MYSQLI_USE_RESULT or MYSQLI_STORE_RESULT depending on the desired behavior. By default, MYSQLI_STORE_RESULT is used. |
Example
尝试使用以下示例来删除表中的记录 -
Try the following example to delete a record in a table −
将以下示例复制粘贴为 mysql_example.php：
Copy and paste the following example as mysql_example.php −
<html>
<head>
<title>Deleting MySQL Table record</title>
</head>
<body>
<?php
$dbhost = 'localhost';
$dbuser = 'root';
$dbpass = 'root@123';
$dbname = 'TUTORIALS';
$mysqli = new mysqli($dbhost, $dbuser, $dbpass, $dbname);
if($mysqli→connect_errno ) {
printf("Connect failed: %s<br />", $mysqli→connect_error);
exit();
}
printf('Connected successfully.<br />');
if ($mysqli→query('DELETE FROM tutorials_tbl where tutorial_id = 4')) {
printf("Table tutorials_tbl record deleted successfully.<br />");
}
if ($mysqli→errno) {
printf("Could not delete record from table: %s<br />", $mysqli→error);
}
$sql = "SELECT tutorial_id, tutorial_title, tutorial_author, submission_date FROM tutorials_tbl";
$result = $mysqli→query($sql);
if ($result→num_rows > 0) {
while($row = $result→fetch_assoc()) {
printf("Id: %s, Title: %s, Author: %s, Date: %d <br />",
$row["tutorial_id"],
$row["tutorial_title"],
$row["tutorial_author"],
$row["submission_date"]);
}
} else {
printf('No record found.<br />');
}
mysqli_free_result($result);
$mysqli→close();
?>
</body>
</html>Output
访问在 apache web 服务器上部署的 mysql_example.php，并验证输出。在运行选择脚本之前，我们在此表中输入了多条记录。
Access the mysql_example.php deployed on apache web server and verify the output. Here we’ve entered multiple records in the table before running the select script.
Connected successfully.
Table tutorials_tbl record deleted successfully.
Id: 1, Title: MySQL Tutorial, Author: Mahesh, Date: 2021
Id: 2, Title: HTML Tutorial, Author: Mahesh, Date: 2021
Id: 3, Title: PHP Tutorial, Author: Mahesh, Date: 2021
Id: 5, Title: Apache Tutorial, Author: Suresh, Date: 2021MySQLi - 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
PHP 使用 mysqli query() 或 mysql_query() 函数使用 Like 子句来选择 MySQL 表中的记录。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 mysqli query() or mysql_query() function to select records in a MySQL table using Like clause. This function takes two parameters and returns TRUE on success or FALSE on failure.
Syntax
$mysqli→query($sql,$resultmode)Sr.No. |
Parameter & Description |
1 |
$sql Required - SQL query to select records in a MySQL table using Like Clause. |
2 |
$resultmode Optional - Either the constant MYSQLI_USE_RESULT or MYSQLI_STORE_RESULT depending on the desired behavior. By default, MYSQLI_STORE_RESULT is used. |
Example
尝试以下示例，以在表中使用 like 子句选择记录 -
Try the following example to select a record using like clause in a table −
将以下示例复制粘贴为 mysql_example.php：
Copy and paste the following example as mysql_example.php −
<html>
<head>
<title>Using Like Clause</title>
</head>
<body>
<?php
$dbhost = 'localhost';
$dbuser = 'root';
$dbpass = 'root@123';
$dbname = 'TUTORIALS';
$mysqli = new mysqli($dbhost, $dbuser, $dbpass, $dbname);
if($mysqli→connect_errno ) {
printf("Connect failed: %s<br />", $mysqli→connect_error);
exit();
}
printf('Connected successfully.<br />');
$sql = 'SELECT tutorial_id, tutorial_title, tutorial_author, submission_date FROM tutorials_tbl where tutorial_author like "Mah%"';
$result = $mysqli→query($sql);
if ($result→num_rows > 0) {
while($row = $result→fetch_assoc()) {
printf("Id: %s, Title: %s, Author: %s, Date: %d <br />",
$row["tutorial_id"],
$row["tutorial_title"],
$row["tutorial_author"],
$row["submission_date"]);
}
} else {
printf('No record found.<br />');
}
mysqli_free_result($result);
$mysqli→close();
?>
</body>
</html>Output
访问在 apache web 服务器上部署的 mysql_example.php，并验证输出。在运行选择脚本之前，我们在此表中输入了多条记录。
Access the mysql_example.php deployed on apache web server and verify the output. Here we’ve entered multiple records in the table before running the select script.
Connected successfully.
Id: 1, Title: MySQL Tutorial, Author: Mahesh, Date: 2021
Id: 2, Title: HTML Tutorial, Author: Mahesh, Date: 2021
Id: 3, Title: PHP Tutorial, Author: Mahesh, Date: 2021MySQLi - 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
PHP 使用 mysqli query() 或 mysql_query() 函数从 MySQL 表中获取排序记录。这个函数接收两个参数，并在成功时返回 TRUE，并在失败时返回 FALSE。
PHP uses mysqli query() or mysql_query() function to get sorted records from a MySQL table. This function takes two parameters and returns TRUE on success or FALSE on failure.
Syntax
$mysqli→query($sql,$resultmode)Sr.No. |
Parameter & Description |
1 |
$sql Required - SQL query to get sorted records from a table. |
2 |
$resultmode Optional - Either the constant MYSQLI_USE_RESULT or MYSQLI_STORE_RESULT depending on the desired behavior. By default, MYSQLI_STORE_RESULT is used. |
Example
尝试使用以下示例从表中获取排序记录 -
Try the following example to get sorted records from a table −
将以下示例复制粘贴为 mysql_example.php：
Copy and paste the following example as mysql_example.php −
<html>
<head>
<title>Sorting MySQL Table records</title>
</head>
<body>
<?php
$dbhost = 'localhost';
$dbuser = 'root';
$dbpass = 'root@123';
$dbname = 'TUTORIALS';
$mysqli = new mysqli($dbhost, $dbuser, $dbpass, $dbname);
if($mysqli→connect_errno ) {
printf("Connect failed: %s<br />", $mysqli→connect_error);
exit();
}
printf('Connected successfully.<br />');
$sql = "SELECT tutorial_id, tutorial_title, tutorial_author, submission_date FROM tutorials_tbl order by tutorial_title asc";
$result = $mysqli→query($sql);
if ($result→num_rows > 0) {
while($row = $result→fetch_assoc()) {
printf("Id: %s, Title: %s, Author: %s, Date: %d <br />",
$row["tutorial_id"],
$row["tutorial_title"],
$row["tutorial_author"],
$row["submission_date"]);
}
} else {
printf('No record found.<br />');
}
mysqli_free_result($result);
$mysqli→close();
?>
</body>
</html>Output
访问部署在 Apache Web 服务器上的 mysql_example.php, 并验证输出。
Access the mysql_example.php deployed on apache web server and verify the output.
Connected successfully.
Id: 5, Title: Apache Tutorial, Author: Suresh, Date: 2021
Id: 2, Title: HTML Tutorial, Author: Mahesh, Date: 2021
Id: 1, Title: MySQL Tutorial, Author: Mahesh, Date: 2021
Id: 3, Title: PHP Tutorial, Author: Mahesh, Date: 2021MySQLi - Using 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
PHP 使用 mysqli query() 或 mysql_query() 函数来使用联接从 MySQL 表中获取记录。这个函数接收两个参数，并在成功时返回 TRUE，并在失败时返回 FALSE。
PHP uses mysqli query() or mysql_query() function to get records from a MySQL tables using Joins. This function takes two parameters and returns TRUE on success or FALSE on failure.
Syntax
$mysqli→query($sql,$resultmode)Sr.No. |
Parameter & Description |
1 |
$sql Required - SQL query to get records from multiple tables using Join. |
2 |
$resultmode Optional - Either the constant MYSQLI_USE_RESULT or MYSQLI_STORE_RESULT depending on the desired behavior. By default, MYSQLI_STORE_RESULT is used. |
首先使用以下脚本在 MySQL 中创建表并插入两条记录。
First create a table in MySQL using following script and insert two records.
create table tcount_tbl(
tutorial_author VARCHAR(40) NOT NULL,
tutorial_count int
);
insert into tcount_tbl values('Mahesh', 3);
insert into tcount_tbl values('Suresh', 1);Example
尝试以下示例以使用连接获取两个表中的记录。−
Try the following example to get records from a two tables using Join. −
将以下示例复制粘贴为 mysql_example.php：
Copy and paste the following example as mysql_example.php −
<html>
<head>
<title>Using joins on MySQL Tables</title>
</head>
<body>
<?php
$dbhost = 'localhost';
$dbuser = 'root';
$dbpass = 'root@123';
$dbname = 'TUTORIALS';
$mysqli = new mysqli($dbhost, $dbuser, $dbpass, $dbname);
if($mysqli→connect_errno ) {
printf("Connect failed: %s<br />", $mysqli→connect_error);
exit();
}
printf('Connected successfully.<br />');
$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';
$result = $mysqli→query($sql);
if ($result→num_rows > 0) {
while($row = $result→fetch_assoc()) {
printf("Id: %s, Author: %s, Count: %d <br />",
$row["tutorial_id"],
$row["tutorial_author"],
$row["tutorial_count"]);
}
} else {
printf('No record found.<br />');
}
mysqli_free_result($result);
$mysqli→close();
?>
</body>
</html>Output
访问部署在 Apache Web 服务器上的 mysql_example.php, 并验证输出。
Access the mysql_example.php deployed on apache web server and verify the output.
Connected successfully.
Id: 1, Author: Mahesh, Count: 3
Id: 2, Author: Mahesh, Count: 3
Id: 3, Author: Mahesh, Count: 3
Id: 5, Author: Suresh, Count: 1MySQL 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.
MySQLi - Handling 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.
以下示例从外部获取 tutorial_count，然后将其与表中可用值进行比较。
The following example takes the tutorial_count from outside and then compares it with the value available in the table.
Example
将以下示例复制粘贴为 mysql_example.php：
Copy and paste the following example as mysql_example.php −
<html>
<head>
<title>Handling NULL</title>
</head>
<body>
<?php
$dbhost = 'localhost';
$dbuser = 'root';
$dbpass = 'root@123';
$dbname = 'TUTORIALS';
$mysqli = new mysqli($dbhost, $dbuser, $dbpass, $dbname);
$tutorial_count = null;
if($mysqli→connect_errno ) {
printf("Connect failed: %s<br />", $mysqli→connect_error);
exit();
}
printf('Connected successfully.<br />');
if( isset($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 NULL';
}
$result = $mysqli→query($sql);
if ($result→num_rows > 0) {
while($row = $result→fetch_assoc()) {
printf("Author: %s, Count: %d <br />",
$row["tutorial_author"],
$row["tutorial_count"]);
}
} else {
printf('No record found.<br />');
}
$mysqli→close();
?>
</body>
</html>MySQLi - 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.
PERL Example
# Get all the tables available in current database.
my @tables = $dbh→tables ( );
foreach $table (@tables ){
print "Table Name $table\n";
}PHP Example
尝试以下示例以获取数据库信息 −
Try the following example to get database info −
将以下示例复制粘贴为 mysql_example.php：
Copy and paste the following example as mysql_example.php −
<html>
<head>
<title>Getting MySQL Database Info</title>
</head>
<body>
<?php
$dbhost = 'localhost';
$dbuser = 'root';
$dbpass = 'root@123';
$dbname = 'TUTORIALS';
$mysqli = new mysqli($dbhost, $dbuser, $dbpass, $dbname);
$tutorial_count = null;
if($mysqli→connect_errno ) {
printf("Connect failed: %s<br />", $mysqli→connect_error);
exit();
}
printf('Connected successfully.<br />');
if ($result = mysqli_query($mysqli, "SELECT DATABASE()")) {
$row = mysqli_fetch_row($result);
printf("Default database is %s<br />", $row[0]);
mysqli_free_result($result);
}
$mysqli→close();
?>
</body>
</html>Output
访问部署在 Apache Web 服务器上的 mysql_example.php, 并验证输出。
Access the mysql_example.php deployed on apache web server and verify the output.
Connected successfully.
Default database is tutorialsGetting Server Metadata
MySQL 中有几个重要命令可以在 MySQL 提示符处执行，也可以使用 PHP 等任何脚本来获取有关数据库服务器的各种重要信息。
There are a few important commands in MySQL which can be executed either at the MySQL prompt or by using any script like PHP to get various important information about the database server.
Sr.No. |
Command & Description |
1 |
SELECT VERSION( ) Server version string |
2 |
SELECT DATABASE( ) Current database name (empty if none) |
3 |
SELECT USER( ) Current username |
4 |
SHOW STATUS Server status indicators |
5 |
SHOW VARIABLES Server configuration variables |
MySQLi - Installation
Downloading MySQL
MySQLi 扩展旨在与 MySQL 4.1.13 版或更高版本配合使用，因此必须下载 MySQL。所有 MySQL 下载内容均位于 MySQL Downloads 。选择您需要的 MySQL Community Server 的最新版本号，并尽可能准确地选择您需要的平台。
The MySQLi extension is designed to work with MySQL version 4.1.13 or newer, So have to download MySQL. All downloads for MySQL are located at MySQL Downloads. Pick the latest version number for MySQL Community Server you want and, as exactly as possible, the platform you want.
Installing MySQL on Linux/UNIX
在 Linux 系统上安装 MySQL 的推荐方式是通过 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 web site −
-
MySQL − The MySQL database server, which manages databases and tables, controls user access, and processes SQL queries.
-
MySQL-client − MySQL client programs, which make it possible to connect to and interact with the server.
-
MySQL-devel − Libraries and header files that come in handy when compiling other programs that use MySQL.
-
MySQL-shared − Shared libraries for the MySQL client.
-
MySQL-bench − Benchmark and performance testing tools for the MySQL database server.
此处列出的 MySQL RPM 都是在 SuSE Linux 系统上构建的，但通常可在其他 Linux 版本上轻松工作。
The MySQL RPMs listed here are all built on a SuSE Linux system, but they’ll usually work on other Linux variants with no difficulty.
现在，按以下步骤继续安装 −
Now, follow the following steps to proceed for installation −
-
Login to the system using root user.
-
Switch to the directory containing the RPMs −
-
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-
This is 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，在任何版本的 Windows 上进行默认安装比以前容易得多，因为 MySQL 现在已与安装程序很好地打包在一起。只需下载安装程序包，将其解压缩到任何位置，然后运行 setup.exe。
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 setup.exe.
默认安装程序 setup.exe 将引导您完成琐碎的进程，并且默认情况下将把所有内容安装在 C:\mysql 下。
Default installer setup.exe will walk you through the trivial process and by default will install everything under C:\mysql.
通过从命令提示符中首次启动服务器来测试服务器。转到可能是 C:\mysql\bin 的 mysqld 服务器位置，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，您会看到一些有关启动和 InnoDB 的消息。如果不是，您可能有权限问题。确保储存数据的目录对数据库进程运行所在的任何用户（可能是 mysql）都是可访问的。
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
在成功安装 MySQL、初始化基本表以及启动服务器后，您可以通过一些简单的测试来验证一切是否应正常工作。
After MySQL has been successfully installed, the base tables have been initialized, and the server has been started, you can verify that all is working as it should via some simple tests.
Use the mysqladmin Utility to Obtain Server Status
使用 mysqladmin 二进制文件检查服务器版本。此二进制文件在 Linux 上的 /usr/bin 中和 Windows 上的 C:\mysql\bin 中可用。
Use mysqladmin binary to check 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如果您没有收到这样的消息，那么您的安装可能存在一些问题，您需要一些帮助来解决它。
If you do not get such message, then there may be some problem in your installation and you would need some help to fix it.
Execute simple SQL commands using MySQL Client
您可以使用 MySQL 客户端通过使用 mysql 命令连接到 MySQL 服务器。此刻，您无需提供任何密码，因为默认情况下将设置为空白。
You can connect to your MySQL server by using MySQL client using mysql command. At this moment, you do not need to give any password as by default it will be set to blank.
因此，只需使用以下命令
So just use following command
[root@host]# mysql它应该会得到一个 mysql> 提示符。现在，您已连接到 MySQL 服务器，并且可以按以下方式在 mysql> 提示符处执行所有 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 command at mysql> prompt as follows −
mysql> SHOW DATABASES;
+----------+
| Database |
+----------+
| mysql |
| test |
+----------+
2 rows in set (0.13 sec)Post-installation Steps
MySQL 将一个空白的密码用于根 MySQL 用户。一旦你成功安装了数据库和客户端，你就需要按如下方式设置根密码 −
MySQL ships with a blank password for the root MySQL user. As soon as you have successfully installed the database and client, you need to set a root password as follows −
[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 用户还希望将你的 MySQL 目录放在你的 PATH 中，这样你就不必在每次想要使用命令行客户端时输入全部路径。对于 bash，它将是类似下列的内容 −
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 every time you want to use the command-line client. For bash, it would be something like −
export PATH = $PATH:/usr/bin:/usr/sbinRunning MySQL at boot time
如果你想在启动时运行 MySQL 服务器，那么确保你有在 /etc/rc.local 文件中的条目。
If you want to run MySQL server at boot time, then make sure you have following entry in /etc/rc.local file.
/etc/init.d/mysqld start此外，你应该在 /etc/init.d/ 目录中有 mysqld 二进制文件。
Also,you should have mysqld binary in /etc/init.d/ directory.
MySQLi - 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.
-
Select_priv
-
Insert_priv
-
Update_priv
-
Delete_priv
-
Create_priv
-
Drop_priv
-
Reload_priv
-
Shutdown_priv
-
Process_priv
-
File_priv
-
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.
MySQLi - Data Types
在表格中正确定义字段对于你的数据库的总体优化非常重要。你应该仅使用你真正需要使用的类型和字段大小；如果你知道你仅将使用 2 个字符，请不要定义一个 10 个字符宽的字段。这些类型的字段（或列）也被称为数据类型，根据你将在那些字段中存储的内容。
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; don’t define a field as 10 characters wide if you know you’re only going to use 2 characters. These types 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，分为三种类别：数值、日期和时间，以及字符串类型。
MySQL uses many different data types broken into three categories: numeric, date and time, and string types.
Numeric Data Types
MySQL 使用所有标准 ANSI SQL 数值数据类型，所以如果你从一个不同的数据库系统来到 MySQL，那么这些定义对你来说看起来将很熟悉。下面的列表显示了常见的数值数据类型和它们的描述 −
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. 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 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 的日期和时间数据类型为 −
The MySQL date and time datatypes are −
-
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 1, 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 HH:MM:SS format.
-
YEAR(M) − Stores a year in 2-digit or 4-digit format. If the length is specified as 2 (for example YEAR(2)), YEAR can be 1970 to 2069 (70 to 69). If the length is specified as 4, 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，但你将存储的大多数数据将为字符串格式。此列表描述了 MySQLi 中的常见字符串数据类型。
Although numeric and date types are fun, most data you’ll store will be in string format. This list describes the common string datatypes in MySQLi.
-
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 sorts and comparisons on 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.
MySQLi - Regexps
您已使用 LIKE …% 看到 MySQL 模式匹配。MySQL 支持另一种基于正则表达式和 REGEXP 运算符的模式匹配操作。如果您熟悉 PHP 或 PERL，那么对您来说理解起来很简单，因为这种匹配与那些脚本正则表达式非常相似。
You have seen MySQL pattern matching with LIKE …%. MySQL supports another type of pattern matching operation based on regular expressions and the REGEXP operator. If you are aware of PHP or PERL, then it’s very simple for you to understand because this matching is very similar to those scripting regular expressions.
以下是可与 REGEXP 运算符一起使用的模式表。
Following is the table of pattern, which can be used along with REGEXP operator.
Pattern |
What the pattern matches |
^ |
Beginning of string |
$ |
End of string |
. |
Any single character |
[…] |
Any character listed between the square brackets |
[^…] |
Any character not listed between the square brackets |
p1 |
p2 |
p3 |
Alternation; matches any of the patterns p1, p2, or p3 |
* |
Zero or more instances of preceding element |
+ |
One or more instances of preceding element |
{n} |
n instances of preceding element |
{m,n} |
m through n instances of preceding element |
Examples
现在，基于上表，您可以设计各种类型的 SQL 查询以满足您的要求。这里我列出一些供您理解。假设我们有一张名为 tutorials_inf 的表，它有一个名为 name 的字段−
Now based on above table, you can device various type of SQL queries to meet your requirements. Here, I’m listing few for your understanding. Consider we have a table called tutorials_inf and it’s having a field called name −
查找所有以“sa”开头的名称的查询
Query to find all the names starting with 'sa'
mysql> SELECT * FROM tutorials_inf WHERE name REGEXP '^sa';示例输出如下所示 −
The sample output should be like this −
+----+------+
| id | name |
+----+------+
| 1 | sai |
+----+------+
1 row in set (0.00 sec)查找所有以“ai”结尾的名称的查询
Query to find all the names ending with 'ai'
mysql> SELECT * FROM tutorials_inf WHERE name REGEXP 'ai$';示例输出如下所示 −
The sample output should be like this −
+----+------+
| id | name |
+----+------+
| 1 | sai |
+----+------+
1 row in set (0.00 sec)查找包含“a”的所有名称的查询
Query to find all the names, which contain 'a'
mysql> SELECT * FROM tutorials_inf WHERE name REGEXP 'a';示例输出如下所示 −
The sample output should be like this −
+----+-------+
| id | name |
+----+-------+
| 1 | sai |
| 3 | ram |
| 4 | johar |
+----+-------+
3 rows in set (0.00 sec)查找所有以元音开头的名称的查询
Query to find all the names starting with a vowel
mysql> SELECT * FROM tutorials_inf WHERE name REGEXP '^[aeiou]';MySQLi - 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，你会将许多 SQL 查询组合到一个组中，并将它们全部作为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 part of a transaction.
Properties of Transactions
事务具有以下四个标准属性，通常用首字母缩写词 ACID 提到 -
Transactions have the following four standard properties, usually referred to by the acronym ACID −
-
Atomicity − 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 − ensures that the database properly changes states upon a successfully committed transaction.
-
Isolation − enables transactions to operate independently on and transparent to each other.
-
Durability − ensures that the result or effect of a committed transaction persists in case of a system failure.
在 MySQL 中，事务以 BEGIN WORK 语句开始，并以 COMMIT 或 ROLLBACK 语句结束。开始和结束语句之间的 SQLi 命令形成事务的主体。
In MySQL, transactions begin with the statement BEGIN WORK and end with either a COMMIT or a ROLLBACK statement. The SQLi 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），则每个 SQL 语句（在事务中或不在事务中）都被视为一个完整的事务，并在完成后默认提交。当 AUTOCOMMIT 设置为 0，即发出 SET AUTOCOMMIT=0 命令时，后续一系列语句就像一个事务，并且在发出显式 COMMIT 语句之前不会提交任何活动。
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. 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 mysqli_query() 函数在 PHP 中执行这些 SQL 命令。
You can execute these SQL commands in PHP by using mysqli_query() function.
Generic Example on Transaction
这个事件序列与所使用的编程语言无关；逻辑路径可以在用于创建应用程序的任何语言中创建。
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 mysqli_query() 函数在 PHP 中执行这些 SQL 命令。
You can execute these SQL commands in PHP by using mysqli_query() function.
-
Begin transaction by issuing 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 ROLLBACK command, otherwise issue a COMMIT command.
Transaction-Safe Table Types in MySQL
你不能直接使用事务，你可以使用它们，但它们并不安全且不能保证。如果你计划在 MySQL 编程中使用事务，则需要以特殊的方式创建表。有许多类型的表格支持事务，但最受欢迎的表格是 InnoDB 。
You can not use transactions directly, you can but they would not be 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 most popular one is InnoDB.
对 InnoDB 表的支持要求从源代码编译 MySQL 时使用一个特定的编译参数。如果你的 MySQL 版本不支持 InnoDB，请让你的互联网服务提供商构建一个支持 InnoDB 表类型的 MySQL 版本或下载并安装适用于 Windows 或 Linux/UNIX 的 MySQL-Max 二进制分发并使用开发环境中的表类型工作。
Support for InnoDB tables requires a specific compilation parameter when compiling MySQL from 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，只需向表创建语句中添加一个 TYPE = InnoDB 定义即可。例如，以下代码创建一个名为 tutorials_innodb 的 InnoDB 表 -
If your MySQL installation supports InnoDB tables, simply add a TYPE = InnoDB definition to the table creation statement. For example, the following code creates an InnoDB table called tutorials_innodb −
root@host# mysql -u root -p;
Enter password:*******
mysql> use TUTORIALS;
Database changed
mysql> create table tutorials_innodb
→ (
→ tutorial_author varchar(40) NOT NULL,
→ tutorial_count INT
→ ) TYPE = InnoDB;
Query OK, 0 rows affected (0.02 sec)查看以下链接以了解更多信息 - InnoDB
Check the following link to know more about − InnoDB
您可以使用其他表类型，如 GEMINI 或 BDB ，但它取决于您的安装是否支持这两种类型。
You can use other table types like GEMINI or BDB, but it depends on your installation if it supports these two types.
MySQLi - ALTER Command
MySQL ALTER 命令非常有用，当你想更改表格名称、任何表格字段或你想添加或删除表格中的现有列时。
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.
让我们从创建一个名为 tutorials_alter 的表格开始。
Let’s begin with creation of a table called tutorials_alter.
root@host# mysql -u root -p password;
Enter password:*******
mysql> use TUTORIALS;
Database changed
mysql> create table tutorials_alter
→ (
→ i INT,
→ c CHAR(1)
→ );
Query OK, 0 rows affected (0.27 sec)
mysql> SHOW COLUMNS FROM tutorials_alter;
+-------+---------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+---------+------+-----+---------+-------+
| i | int(11) | YES | | NULL | |
| c | char(1) | YES | | NULL | |
+-------+---------+------+-----+---------+-------+
2 rows in set (0.02 sec)Dropping, Adding or Repositioning a Column
假设您想放弃上面 MySQL 表的现有列 i ，那么您将按照如下所示，使用 DROP 子句和 ALTER 命令 −
Suppose you want to drop an existing column i from above MySQL table then you will use DROP clause along with ALTER command as follows −
mysql> ALTER TABLE tutorials_alter DROP i;当列是表格中仅剩的一列时， DROP 不会起作用。
A DROP will not work if the column is the only one left in the table.
要添加列，请使用 ADD 并指定列定义。以下语句将 i 列还原到教程_更改 −
To add a column, use ADD and specify the column definition. The following statement restores the i column to tutorials_alter −
mysql> ALTER TABLE tutorials_alter ADD i INT;发出此语句后，testalter 将包含与您首次创建表时相同的两列，但结构不会完全相同。这是因为默认情况下会将新列添加到表的末尾。因此，即使 i 最初是 mytbl 中的第一列，现在它也是最后一列了。
After issuing this statement, testalter will contain the same two columns that it had when you first created the table, but will not have quite the same structure. That’s because new columns 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 tutorials_alter;
+-------+---------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+---------+------+-----+---------+-------+
| c | char(1) | YES | | NULL | |
| i | int(11) | YES | | NULL | |
+-------+---------+------+-----+---------+-------+
2 rows in set (0.01 sec)要指示您要在表的特定位置放置一列，请使用 FIRST 使其成为第一列，或使用 AFTER col_name 指示将新列置于 col_name 之后。试用一下以下 ALTER TABLE 语句，并在每个语句后使用 SHOW COLUMNS 来查看每个语句有什么效果 −
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 col_name. 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 限定符仅适用于 ADD 子句。这意味着如果您想重新定位表中现有的列，则必须先将其 DROP，然后在新的位置将其 ADD。
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.
Changing a Column Definition or Name
要更改列的定义，请使用 MODIFY 或 CHANGE 子句以及 ALTER 命令。例如，要将列 c 从 CHAR(1) 更改为 CHAR(10)，请这样做 −
To change a column’s definition, use MODIFY or CHANGE clause along with ALTER command. For example, to change column c from CHAR(1) to CHAR(10), do this −
mysql> ALTER TABLE tutorials_alter MODIFY c CHAR(10);使用 CHANGE 时，语法有些不同。在 CHANGE 关键字后面，您命名要更改的列，然后指定新定义，其中包括新名称。试用以下示例：
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. Try out the following example:
mysql> ALTER TABLE tutorials_alter CHANGE i j BIGINT;如果您现在使用 CHANGE 将 j 从 BIGINT 转换回 INT 而无需更改列名，则语句将按预期的那样 −
If you now use CHANGE to convert j from BIGINT back to INT without changing the column name, the statement will be as expected −
mysql> ALTER TABLE tutorials_alter CHANGE j j INT;The Effect of ALTER TABLE on Null and Default Value Attributes −
在 MODIFY 或 CHANGE 列时，您还可以指定列是否可以包含 NULL 值以及其默认值是什么。事实上，如果不这样做，MySQL 会自动为这些属性分配值。
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.
以下示例中，NOT NULL 列的默认值为 100。
Here is the example, where NOT NULL column will have value 100 by default.
mysql> ALTER TABLE tutorials_alter
→ MODIFY j BIGINT NOT NULL DEFAULT 100;如果您不使用上述命令，那么 MySQL 将填入所有列中的 NULL 值。
If you don’t use above command, then MySQL will fill up NULL values in all the columns.
Changing a Column’s Default Value
您可以使用 ALTER 命令更改任何列的默认值。试用以下示例。
You can change a default value for any column using ALTER command. Try out the following example.
mysql> ALTER TABLE tutorials_alter ALTER j SET DEFAULT 1000;
mysql> SHOW COLUMNS FROM tutorials_alter;
+-------+------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+------------+------+-----+---------+-------+
| c | char(10) | YES | | NULL | |
| j | bigint(20) | NO | | 1000 | |
+-------+------------+------+-----+---------+-------+
2 rows in set (0.02 sec)您可以使用 DROP 子句和 ALTER 命令从任何列中删除默认约束。
You can remove default constraint from any column by using DROP clause along with ALTER command.
mysql> ALTER TABLE tutorials_alter ALTER j DROP DEFAULT;
mysql> SHOW COLUMNS FROM tutorials_alter;
+-------+------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+------------+------+-----+---------+-------+
| c | char(10) | YES | | NULL | |
| j | bigint(20) | NO | | NULL | |
+-------+------------+------+-----+---------+-------+
2 rows in set (0.02 sec)Changing a Table Type
您可以使用 TYPE 子句和 ALTER 命令使用表类型。
You can use a table type by using TYPE clause along with ALTER command.
要找出表当前的类型，请使用 SHOW TABLE STATUS 语句。
To find out the current type of a table, use the SHOW TABLE STATUS statement.
mysql> SHOW TABLE STATUS LIKE 'tutorials_alter'\G
*************************** 1. row ***************************
Name: tutorials_alter
Engine: InnoDB
Version: 10
Row_format: Compact
Rows: 0
Avg_row_length: 0
Data_length: 16384
Max_data_length: 0
Index_length: 0
Data_free: 0
Auto_increment: NULL
Create_time: 2017-02-17 11:30:29
Update_time: NULL
Check_time: NULL
Collation: latin1_swedish_ci
Checksum: NULL
Create_options:
Comment:
1 row in set (0.00 sec)Renaming a Table
要重命名表，请使用 ALTER TABLE 语句的 RENAME 选项。试用以下示例将 tutorials_alter 重命名为 tutorials_bks。
To rename a table, use the RENAME option of the ALTER TABLE statement. Try out the following example to rename tutorials_alter to tutorials_bks.
mysql> ALTER TABLE tutorials_alter RENAME TO tutorials_bks;您可以使用 ALTER 命令在 MySQL 文件中创建和删除 INDEX。我们将在下一章中看到此功能。
You can use ALTER command to create and drop INDEX on a MySQL file. We will see this feature in next chapter.
MySQLi - 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，应考虑创建 SQL 查询和在这些列上创建或多个索引的列。
While creating index, it should be considered that what are the columns which will be used to make SQL queries and create one or more indexes on those columns.
实际上，索引也是表的一种类型，它保留主键或索引字段和指向实际表中每条记录的指针。
Practically, indexes are also 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，它们仅用于加速查询，并将由数据库搜索引擎用来非常快速地查找记录。
The users cannot see the indexes, they are just used to speed up queries and will be used by Database Search Engine to locate records very fast.
INSERT 和 UPDATE 语句在具有索引的表上花费更多时间，而 SELECT 语句在这些表上变得快速。原因是在执行插入或更新时，数据库也需要插入或更新索引值。
INSERT and UPDATE statements take more time on tables having indexes where as SELECT statements become fast on those tables. The reason is that while doing insert or update, database need to insert or update 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,...);你可以使用一列或多列来创建索引。例如，我们可以使用 NAME_INDEX 在 tutorials_inf 上创建一个索引。
You can use one or more columns to create an index. For example, we can create an index on tutorials_inf using NAME_INDEX.
CREATE UNIQUE INDEX NAME_INDEX ON tutorials_inf(name);你可以在表上创建一个简单索引。只需从查询中省略 UNIQUE 关键字即可创建简单索引。简单索引允许表中有重复值。
You can create a simple index on a table. Just omit UNIQUE keyword from the query to create simple index. Simple index allows duplicate values in a table.
如果你想按降序对列中的值进行索引，可以在列名后添加保留字 DESC。
If you want to index the values in a column in descending order, you can add the reserved word DESC after the column name.
mysql> CREATE UNIQUE INDEX NAME_INDEX ON tutorials_inf (name 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 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 values must be unique (with the exception of 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.
以下是将索引添加到现有表中的示例。
Here is the example to add index in an existing table.
mysql> ALTER TABLE tutorials_inf ADD INDEX (id);你还可以使用 DROP 子句和 ALTER 命令以相同的方式删除主键。尝试以下示例以删除上述创建的索引。
You can drop any INDEX by using DROP clause along with ALTER command. Try out the following example to drop above-created index.
mysql> ALTER TABLE tutorials_inf DROP INDEX (c);你还可以使用 DROP 子句和 ALTER 命令以相同的方式删除主键。尝试以下示例以删除上述创建的索引。
You can drop any INDEX by using DROP clause along with ALTER command. Try out the following example to drop above-created index.
ALTER Command to add and drop PRIMARY KEY
你也可以添加主键。但请确保主键作用于 NOT NULL 列。
You can add primary key as well in the same way. But make sure Primary Key works on columns, which are NOT NULL.
以下为向现有表格添加主键的示例。这将首先使列成为非空，再将其添加为主键。
Here is the example to add 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 tutorials_inf MODIFY id INT NOT NULL;
mysql> ALTER TABLE tutorials_inf ADD PRIMARY KEY (id);您可以使用 ALTER 命令放弃主键，如下所示：
You can use ALTER command to drop a primary key as follows:
mysql> ALTER TABLE tutorials_inf 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
您可以使用 SHOW INDEX 命令列出与表格关联的所有索引。在这种情况下，垂直格式输出（由 \G 指定）通常非常有用，以避免在长行中进行换行−
You can use SHOW INDEX command to list out all the indexes associated with a table. Vertical-format output (specified by \G) often is useful with this statement, to avoid long line wraparound −
尝试以下示例
Try out the following example
mysql> SHOW INDEX FROM table_name\G
........MySQLi - 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.
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
以下示例展示了临时表的使用方法。相同的代码可以使用 mysqli_query() 函数在 PHP 脚本中。
Here is an example showing you usage of temporary table. Same code can be used in PHP scripts using mysqli_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)当您发出 SHOW TABLES 命令时，您的临时表将不会列在列表中。现在，如果您注销 MySQL 会话，然后发出 SELECT 命令，那么您将发现数据库中没有可用数据。即使您的临时表也不存在。
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 would also not exist.
Dropping Temporary Tables
默认情况下，当您的数据库连接终止时，所有临时表将由 MySQL 删除。如果您仍然想在两者之间进行删除，您可以发出 DROP TABLE 命令。
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 DROP TABLE command.
以下是删除临时表的示例 −
Following is the example on dropping a temporary table −
mysql> DROP TABLE SalesSummary;
mysql> SELECT * FROM SalesSummary;
ERROR 1146: Table 'TUTORIALS.SalesSummary' doesn't existMySQLi - Clone Tables
可能存在需要一张表的精确副本的情况，而对于 CREATE TABLE … SELECT 来说，因为副本必须包含相同的索引、默认值等，它并不适合你的目的。
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.
你可以执行以下步骤来处理此类情况−
You can handle this situation by following steps −
-
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 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 tutorials_inf 创建一个克隆表。
Try out the following example to create a clone table for tutorials_inf.
Step 1
获取表的完整结构。
Get complete structure about table.
mysql> SHOW CREATE TABLE tutorials_inf \G;
*************************** 1. row ***************************
Table: tutorials_inf
Create Table: CREATE TABLE `tutorials_inf` (
`id` int(11) NOT NULL,
`name` varchar(20) NOT NULL,
PRIMARY KEY (`id`),
UNIQUE KEY `AUTHOR_INDEX` (`name`),
UNIQUE KEY `NAME_INDEX` (`name`),
KEY `id` (`id`)
) ENGINE = InnoDB DEFAULT CHARSET = latin1
1 row in set (0.05 sec)
ERROR: No query specifiedStep 2
重命名此表并创建另一张表。
Rename this table and create another table.
mysql> CREATE TABLE tutorials_clone(
→ id int(11) NOT NULL,
→ name varchar(20) NOT NULL,
→ PRIMARY KEY (id),
→ UNIQUE KEY AUTHOR_INDEX (name),
→ UNIQUE KEY NAME_INDEX (name),
→ KEY id (id));
Query OK, 0 rows affected (1.80 sec)Step 3
在执行步骤 2 后，你将在自己的数据库中创建一张克隆表。如果你想从旧表中复制数据，可以使用 INSERT INTO… SELECT 语句来执行此操作。
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 tutorials_clone(id,name) SELECT id,name from tutorials_inf;
Query OK, 4 rows affected (0.19 sec)
Records: 4 Duplicates: 0 Warnings: 0最后，你将获得自己想要的一个精确克隆表。
Finally, you will have exact clone table as you wanted to have.
MySQLi - Using Sequences
序列是一组按需生成的整数 1, 2, 3, …。在数据库中经常使用序列，因为许多应用程序要求表格中的每一行都包含一个唯一值，而序列提供了一种简单的生成它们的方法。本章介绍如何在 MySQL 中使用序列。
A sequence is a set of integers 1, 2, 3, … that are generated in order on demand. Sequences are frequently used in databases because many applications require each row in a table to contain a unique value and sequences provide an easy way to generate them. 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个列定义为 AUTO_INCREMENT，并让 MySQL 处理其余的事情。
The simplest way in MySQL to use Sequences is to define a column as AUTO_INCREMENT and leave rest of the things to MySQL to take care.
Example
试一试下面的示例。这将创建表格，在表格中插入几行，而无需提供记录 ID，因为它已由 MySQL 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’s auto incremented by MySQL.
mysql>CREATE TABLE tutorials_auto(
id INT UNSIGNED NOT NULL AUTO_INCREMENT, name VARCHAR(30) NOT NULL,PRIMARY KEY(id));
Query OK, 0 rows affected (0.28 sec)
mysql>INSERT INTO tutorials_auto(id,name) VALUES(NULL,'sai'),(NULL,'ram');
Query OK, 2 rows affected (0.12 sec)
Records: 2 Duplicates: 0 Warnings: 0
mysql> SELECT * FROM insect ORDER BY id;
+----+------+
| id | name |
+----+------+
| 1 | sai |
| 2 | ram |
+----+------+
2 rows in set (0.05 sec)Obtain AUTO_INCREMENT Values
LAST_INSERT_ID() 是一个 SQL 函数，因此您可以从任何理解如何发出 SQL 语句的客户端中使用它。否则，PERL 和 PHP 脚本提供独占功能来检索最后记录的自动递增值。
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 auto incremented value of last record.
PERL Example
使用 mysql_insertid 属性来获取查询生成的 AUTO_INCREMENT 值。此属性可通过数据库句柄或语句句柄访问，具体取决于您如何发出查询。以下示例通过数据库句柄引用它：
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. The following example references it through the database handle:
$dbh→do ("INSERT INTO tutorials_auto (name,date,origin)
VALUES('moth','2001-09-14','windowsill')");
my $seq = $dbh→{mysqli_insertid};PHP Example
发出生成 AUTO_INCREMENT 值的查询后，通过调用 mysql_insert_id() 来检索值 -
After issuing a query that generates an AUTO_INCREMENT value, retrieve the value by calling mysql_insert_id( ) −
mysql_query ("INSERT INTO tutorials_auto (name,date,origin)
VALUES('moth','2001-09-14','windowsill')", $conn_id);
$seq = mysqli_insert_id ($conn_id);Renumbering an Existing Sequence
在您从表中删除许多记录且希望重新排序所有记录时，可能会出现这种情况。这可以通过一个简单的技巧来完成，但如果您的表与其他表具有联接，则在执行此操作时应格外小心。
There may be a case when you have deleted many records from a table and you want to resequence 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 other table.
如果您确定对 AUTO_INCREMENT 列重新排序不可避免，那么执行此操作的方法是从表中删除该列，然后重新添加该列。以下示例展示了如何使用此技术重新编号 insect 表中的 id 值 -
If you determine that resequencing an AUTO_INCREMENT column is unavoidable, the way to do it is to drop the column from the table, then add it again. The following example shows how to renumber the id values in the insect table using this technique −
mysql> ALTER TABLE tutorials_auto DROP id;
mysql> ALTER TABLE tutorials_auto
→ 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，MySQLi 将从 1 开始序列，但您还可以在创建表时指定任何其他数字。以下是 MySQL 将从 100 开始序列的示例。
By default, MySQLi will start sequence from 1 but you can specify any other number as well at the time of table creation. Following is the example where MySQL will start sequence from 100.
mysql> CREATE TABLE tutorials_auto
→ (
→ id INT UNSIGNED NOT NULL AUTO_INCREMENT = 100,
→ PRIMARY KEY (id),
→ name VARCHAR(30) NOT NULL,
→ );或者，你可以创建表，然后使用 ALTER TABLE 设置初始序列值。
Alternatively, you can create the table and then set the initial sequence value with ALTER TABLE.
mysql> ALTER TABLE tutorials_auto AUTO_INCREMENT = 100;MySQLi - Handling Duplicates
表或结果集有时会包含重复记录。有时允许这样做，但有时需要停止重复记录。有时，需要识别重复记录并将其从表中删除。本章将介绍如何防止重复记录出现在表中，以及如何删除已存在的重复记录。
Tables or result sets sometimes contain duplicate records. Sometimes, it is allowed but sometimes it is required to stop duplicate records. Sometimes, it is required to identify duplicate records and remove them from the table. This chapter will describe how to prevent duplicate records occurring in a table and how to remove already existing duplicate records.
Preventing Duplicates from Occurring in a Table
你可以在具有适当字段的表上使用 PRIMARY KEY 或 UNIQUE 索引来停止重复记录。我们举一个例子：下表没有这样的索引或主键，因此它将允许 first_name 和 last_name 出现重复记录。
You can use a PRIMARY KEY or UNIQUE Index on a table with appropriate fields to stop duplicate records. Let’s take one 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)
);若要防止在此表中创建具有相同 first 和 last 名称值的多个记录，请在其定义中添加 PRIMARY KEY。在你这样做的时候，同时有必要声明索引列为 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’s 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 而不是 INSERT 。如果记录不重复现有记录，MySQL 将照常插入它。如果记录是重复的，IGNORE 关键字告诉 MySQL 在不生成错误的情况下默默地丢弃它。
Use INSERT IGNORE rather than INSERT. If a record doesn’t duplicate an existing record, MySQL inserts it as usual. If the record is a duplicate, the IGNORE keyword tells MySQL to discard it silently without generating an error.
下面的例子不会出错，同时也不会插入重复的记录。
Following example does not error out and same time it will not insert duplicate records.
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 而不是 INSERT。如果记录是新的，则会像 INSERT 一样插入它。如果它是重复的，则新记录将替换旧记录 −
Use REPLACE rather than INSERT. If the record is new, it’s inserted just as with INSERT. If it’s 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)应根据你希望施加的重复处理行为选择 INSERT IGNORE 和 REPLACE。INSERT IGNORE 会保留一组重复记录中的第一个，并丢弃其余记录。REPLACE 会保留一组重复记录中的最后一个，并删除任何先前的记录。
INSERT IGNORE and REPLACE should be chosen according to the duplicate-handling behavior you want to effect. INSERT IGNORE keeps the first of a set of duplicated records and discards the rest. REPLACE keeps the last of a set of duplicates and erase out any earlier ones.
强制唯一性的另一种方法是向表中添加 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 表中所有重复记录的列表。一般来说，要识别重复值集，请执行以下操作 −
This query will return a list of all the duplicate records in person_tbl table. In general, to identify sets of values that are duplicated, do the following −
-
Determine which columns contain the values that may be duplicated.
-
List those columns in the column selection list, along with COUNT(*).
-
List the columns in the GROUP BY clause as well.
-
Add a HAVING clause that eliminates unique values by requiring group counts to be greater than one.
Eliminating Duplicates from a Query Result:
你可以将 DISTINCT 与 SELECT 语句一起使用，以查找表中可用的唯一记录。
You can use DISTINCT along with 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;与 DISTINCT 对应的替代方法是添加一个 GROUP BY 子句，该子句命名你正在选择的列。这将起到删除重复项并仅选择指定列中值唯一组合的效果 −
An alternative to DISTINCT is to add a GROUP BY clause that names the columns you’re 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
如果你在表中复制记录并且希望从该表中删除所有重复记录，那么这里有一个过程 -
If you have duplicate records in a table and you want to remove all the duplicate records from that table, then here is the procedure −
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种简单方法是向该表添加 INDEX 或 PRIMAY KEY。即使此表已经可用，你也可以使用此技术来删除重复记录，并且将来你也将安全。
An easy way of removing duplicate records from a table is to add an INDEX or PRIMAY KEY to that table. Even if this table is already available, you can use this technique to remove duplicate records and you will be safe in future as well.
mysql> ALTER IGNORE TABLE person_tbl
→ ADD PRIMARY KEY (last_name, first_name);