MySQL delete 语句

柔情只为你懂 2023-06-27 03:14 14阅读 0赞

mysql 中delete语句主要分为三个层次，下面简单介绍下

1. 最基础的条件删除，如下所示

DELETE FROM table_name  where    table_name.name='dell'

还有一种按序删除的方式如下

DELETE FROM customers ORDER BY Name LIMIT 10

2. MySQL DELETE语句使用INNER JOIN子句

DELETE  a FROM tablename AS a LEFT JOIN temp_name AS b ON a.ID = b.ID WHERE b.UserID > 0;
    
    
    DELETE  a FROM tablename AS a LEFT JOIN temp_name AS b ON a.ID = b.ID WHERE b.ID IS not null;

3. MySQL ON DELETE CASCADE示例

此时 有A和B两个表，当删除A表的记录时，B表关联的字段自动删除，此时需要用到这种方式；

**第一步**， 创建`buildings`表，如下创建语句：

USE testdb;
    CREATE TABLE buildings (
        building_no INT PRIMARY KEY AUTO_INCREMENT,
        building_name VARCHAR(255) NOT NULL,
        address VARCHAR(255) NOT NULL
    )ENGINE=InnoDB DEFAULT CHARSET=utf8;

**第二步**， 创建`rooms`表，如下创建语句：

USE testdb;
    CREATE TABLE rooms (
        room_no INT PRIMARY KEY AUTO_INCREMENT,
        room_name VARCHAR(255) NOT NULL,
        building_no INT NOT NULL,
        FOREIGN KEY (building_no)
            REFERENCES buildings (building_no)
            ON DELETE CASCADE
    )ENGINE=InnoDB DEFAULT CHARSET=utf8;

请注意，在外键约束定义的末尾添加`ON DELETE CASCADE`子句。

第三步插入部分数据

INSERT INTO buildings(building_name,address)
    VALUES('海南大厦','海口市国兴大道1234号'),
          ('万达水城','海口市大同路1200号');
    
    INSERT INTO rooms(room_name,building_no)
    VALUES('Amazon',1),
          ('War Room',1),
          ('Office of CEO',1),
          ('Marketing',2),
          ('Showroom',2);

此时 删除building\_no = 2 的记录，可以看到rooms表中也删除了

DELETE FROM buildings WHERE building_no = 2;

请注意，`ON DELETE CASCADE`仅支持使用存储引擎支持外键(如`InnoDB`)的表上工作。 某些表类型不支持诸如`MyISAM`的外键，因此应该在使用MySQL `ON DELETE CASCADE`引用操作的表上选择适当的存储引擎。