sql语句删除表中重复的数据

mysql> select * from user;
+----+--------+-----+
| id | name   | age |
+----+--------+-----+
|  1 | 张三   |  11 |
|  2 | 张三   |  11 |
|  3 | 李四   |  11 |
+----+--------+-----+
3 rows in set (0.00 sec)

不想看文章的朋友,直接拿去

mysql> delete from user
    -> where id not in
    -> (select * from
    -> (select min(id) from user group by name,age)as a);

试验过程:
预期sql语句

利用group by对同一数据进行分组,利用min(id)的方法找到同一数据的最小id(当然,你想最大也可以,max(id))

select min(id) from user group by name,age;

最后利用not in找到属于重复数据的id,接着删除

mysql> delete from user
    -> where id not in
    -> (select min(id) from user group by name,age);
ERROR 1093 (HY000): You can't specify target table 'user' for update in FROM clause

ERROR 1093 (HY000): You can’t specify target table ‘user’ for update in FROM clause
要求不能对进行查询操作的表进行update操作，也就说我们的where条件中进行了子查询，并且子查询也是针对需要进行update操作的表的，mysql不支持这种查询修改的方式。
经过查询资料,发现可以使用临时表来保存数据以此来规避错误

mysql> delete from user
    -> where id not in
    -> (select * from
    -> (select min(id) from user group by name,age));
ERROR 1248 (42000): Every derived table must have its own alias

ERROR 1248 (42000): Every derived table must have its own alias
要求每一个派生出来的表都必须有一个自己的别名。
参考如下:

Every derived table must have its own alias（sql语句错误解决方法） - KING - CSDN博客
https://blog.csdn.net/qq_32863631/article/details/83024322

简而言之,就是在查询表的后面添加as 别名就可以了
改变一下sql语句
(a表示的是select min(id) from user group by name,age执行后的临时表)

(select * from
    -> (select min(id) from user group by name,age)as a);

所以,最后的sql语句就完成了

mysql> delete from user
    -> where id not in
    -> (select * from
    -> (select min(id) from user group by name,age)as a);
Query OK, 0 rows affected (0.00 sec)
mysql> select * from user;
+----+--------+-----+
| id | name   | age |
+----+--------+-----+
|  1 | 张三   |  11 |
|  3 | 李四   |  11 |
+----+--------+-----+
2 rows in set (0.00 sec)