mysql之exists子查询_MySQL

mysql之exists子查询

子查询可以分为：from where 和 exists子查询

分类表：

[sql]

mysql> select * from category;

+----+---------+

| id | c_name |

+----+---------+

| 1 | ios |

| 2 | android |

| 3 | sb |

+----+---------+

3 rows in set

商品表：

[sql]

mysql> select * from goods;

+----+---------+--------+-------+-----+

| id | name | cat_id | price | num |

+----+---------+--------+-------+-----+

| 1 | 苹果 | 1 | 4999 | 2 |

| 2 | nexus4 | 2 | 1999 | 3 |

| 4 | 荣耀2 | 2 | 1888 | 5 |

| 6 | 三星 | 2 | 3000 | 2 |

+----+---------+--------+-------+-----+

6 rows in se

要求：只找出分类下有商品的分类

[sql]

mysql> select * from category c where exists (select * from goods where cat_id=c.id);

+----+---------+

| id | c_name |

+----+---------+

| 1 | ios |

| 2 | android |

+----+---------+

2 rows in set