MySQL delete 语句_web15286201346_mysql删除语句

大大的周 02-07 8048

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。