MySQL 删除重复数据

例如，id 为主键，a 列有重复数据，想要删除 重复的a，即a相同的只保留一行，可以试试如下查询：

select * from test where id not in (select max(id) from test group by a);

把 select * 换成 delete 就是删除了

mysql> select * from test;
+------+------+------+------+
| id   | a    | b    | c    |
+------+------+------+------+
|    1 |    1 |    1 |    1 |
|    2 |    1 |    2 |    2 |
|    3 |    2 |    2 |    2 |
|    4 |    3 |    3 |    3 |
|    5 |    3 |    5 |    5 |
|    6 |    3 |    6 |    6 |
+------+------+------+------+
6 rows in set (0.12 sec)

mysql> select * from test where id not in (select max(id) from test group by a);
+------+------+------+------+
| id   | a    | b    | c    |
+------+------+------+------+
|    1 |    1 |    1 |    1 |
|    4 |    3 |    3 |    3 |
|    5 |    3 |    5 |    5 |
+------+------+------+------+
3 rows in set (0.12 sec)

mysql>