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📜  Python MySQL-删除数据

📅  最后修改于: 2020-11-07 07:42:25             🧑  作者: Mango

要从MySQL表中删除记录，您需要使用DELETE FROM语句。要删除特定记录，您需要与其一起使用WHERE子句。

句法

以下是MYSQL中DELETE查询的语法-

DELETE FROM table_name [WHERE Clause]

例

假设我们已经在MySQL中创建了一个名为EMPLOYEES的表-

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)

如果我们使用INSERT语句将4条记录插入到其中-

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语句删除带有FIRST_NAME“ Mac”的员工的记录。

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

如果您检索该表的内容，由于我们已删除一条记录，因此只能看到3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)

如果执行不带WHERE子句的DELETE语句，则指定表中的所有记录将被删除。

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

如果检索表的内容，将得到一个空集，如下所示-

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

使用Python删除表的记录

要从数据库中删除某些记录时，需要执行DELETE操作。

删除表中的记录-

  • 导入mysql.connector包。

  • 使用mysql.connector.connect()方法创建连接对象，方法是将用户名，密码，主机(可选的默认值：localhost)和数据库(可选的)作为参数传递给它。

  • 通过在上面创建的连接对象上调用cursor()方法来创建游标对象。

  • 然后，通过将DELETE语句作为参数传递给execute()方法来执行它。

例

以下程序从AGE大于20的EMPLOYEE中删除所有记录-

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()

输出

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)
]