MySQL联表查询及联表删除的方法

MySQL联表查询及联表删除都是经常需要用到的操作,下面对MySQL联表查询和联表删除都作了详细的介绍分析,希望对您有所帮助。

MySQL联表查询:

reference mysql manul:
3.2.7. SELECT语法13.2.7.1. JOIN语法
13.2.7.2. UNION语法
eg1:·mysql> SELECT t1.name, t2.salary FROM employee AS t1, info AS t2·->    WHERE t1.name = t2.name;eg2:·mysql> SELECT table1.* FROM table1·->        LEFT JOIN table2 ON table1.id=table2.id·->        WHERE table2.id IS NULL;

联表删除:

1、从数据表t1 中把那些id值在数据表t2 里有匹配的记录全删除掉

DELETE t1 FROM t1,t2 WHERE t1.id=t2.id    或DELETE  FROM t1 USING t1,t2 WHERE t1.id=t2.id

2、从数据表t1里在数据表t2里没有匹配的记录查找出来并删除掉

DELETE t1 FROM t1 LEFT JOIN T2 ON t1.id=t2.id WHERE t2.id IS NULL 或

DELETE  FROM t1,USING t1 LEFT JOIN T2 ON t1.id=t2.id WHERE t2.id IS NULL

3、从两个表中找出相同记录的数据并把两个表中的数据都删除掉

DELETE t1,t2 from t1 LEFT JOIN t2 ON t1.id=t2.id WHERE t1.id=25

注意此处的delete t1,t2 from 中的t1,t2不能是别名

如:delete t1,t2 from table_name as t1 left join table2_name as t2 on t1.id=t2.id where table_name.id=25 在数据里面执行是错误的(MYSQL 版本不小于5.0在5.0中是可以的)

上述语句改写成

delete table_name,table2_name from table_name as t1 left join table2_name as t2 on t1.id=t2.id where table_name.id=25 在数据里面执行是错误的(MYSQL 版本小于5.0在5.0中是可以的)

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