MySQL delete 语句

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。