Python Data Access 简明教程

Python MySQL - Delete Data

要从 MySQL 表格中删除记录,需要使用 DELETE FROM 语句。要移除特定记录,需要同时使用 WHERE 子句。

Syntax

以下是 MYSQL 中 DELETE 查询的语法:

DELETE FROM table_name [WHERE Clause]

Example

假设我们在 MySQL 中使用 EMPLOYEES 作为名称创建了一个表格,如下所示:

mysql> CREATE TABLE EMPLOYEE(
   FIRST_NAME CHAR(20) NOT NULL,
   LAST_NAME CHAR(20),
   AGE INT,
   SEX CHAR(1),
   INCOME FLOAT
);
Query OK, 0 rows affected (0.36 sec)

如果使用 INSERT 语句向其中插入了 4 条记录,如下所示:

mysql> INSERT INTO EMPLOYEE VALUES
   ('Krishna', 'Sharma', 19, 'M', 2000),
   ('Raj', 'Kandukuri', 20, 'M', 7000),
   ('Ramya', 'Ramapriya', 25, 'F', 5000),
   ('Mac', 'Mohan', 26, 'M', 2000);

以下 MySQL 语句删除了 FIRST_NAME 为“Mac”的员工记录。

mysql> DELETE FROM EMPLOYEE WHERE FIRST_NAME = 'Mac';
Query OK, 1 row affected (0.12 sec)

如果检索表格内容,可以看到只有 3 条记录,因为我们删除了一条记录。

mysql> select * from EMPLOYEE;
+------------+-----------+------+------+--------+
| FIRST_NAME | LAST_NAME | AGE  | SEX  | INCOME |
+------------+-----------+------+------+--------+
| Krishna    | Sharma    | 20   | M    | 2000   |
| Raj        | Kandukuri | 21   | M    | 7000   |
| Ramya      | Ramapriya | 25   | F    | 5000   |
+------------+-----------+------+------+--------+
3 rows in set (0.00 sec)

如果没有 WHERE 子句,执行 DELETE 语句会删除指定表格中的所有记录。

mysql> DELETE FROM EMPLOYEE;
Query OK, 3 rows affected (0.09 sec)

如果检索表格内容,将获取如下所示的空集:

mysql> select * from EMPLOYEE;
Empty set (0.00 sec)

Removing records of a table using python

当需要从数据库删除某些记录时,需要 DELETE 操作。

要删除表格中的记录:

  1. import mysql.connector package.

  2. 使用 mysql.connector.connect() 方法创建一个连接对象,通过将用户名、密码、主机(可选,默认值:localhost)和数据库(可选)作为参数传递给该对象。

  3. 通过对上面创建的连接对象调用 cursor() 方法创建一个游标对象。

  4. 然后,通过将 DELETE 语句作为参数传递给 execute() 方法执行该语句。

Example

以下程序删除了 EMPLOYEE 中 AGE 超过 20 岁的所有记录:

import mysql.connector

#establishing the connection
conn = mysql.connector.connect(
   user='root', password='password', host='127.0.0.1', database='mydb')

#Creating a cursor object using the cursor() method
cursor = conn.cursor()

#Retrieving single row
print("Contents of the table: ")
cursor.execute("SELECT * from EMPLOYEE")
print(cursor.fetchall())

#Preparing the query to delete records
sql = "DELETE FROM EMPLOYEE WHERE AGE > '%d'" % (25)

try:
   # Execute the SQL command
   cursor.execute(sql)

   # Commit your changes in the database
   conn.commit()
except:
   # Roll back in case there is any error
   conn.rollback()

#Retrieving data
print("Contents of the table after delete operation ")
cursor.execute("SELECT * from EMPLOYEE")
print(cursor.fetchall())

#Closing the connection
conn.close()

Output

Contents of the table:
[('Krishna', 'Sharma', 22, 'M', 2000.0),
   ('Raj', 'Kandukuri', 23, 'M', 7000.0),
   ('Ramya', 'Ramapriya', 26, 'F', 5000.0),
   ('Mac', 'Mohan', 20, 'M', 2000.0),
   ('Ramya', 'Rama priya', 27, 'F', 9000.0)]

Contents of the table after delete operation:
[('Krishna', 'Sharma', 22, 'M', 2000.0),
   ('Raj', 'Kandukuri', 23, 'M', 7000.0),
   ('Mac', 'Mohan', 20, 'M', 2000.0)]