你这个问题是否可以理解为“验证表里的某一不确定的字段的值，没有重复”？

如果是的话，那么你就可以先查出表的总记录数，然后在查出该字段去重之后的总记录数，

对比两次结果，如果数量相同则没有重复；如果数量不相等，则代表有重复的内容。

下面是一个示例：

mysql> select * from user;

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

| id | name | address |

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

| 1 | aaa | beijing |

| 2 | bbb | shanghai |

| 3 | ccc | hangzhou |

| 5 | aaa | chongqing |

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

4 rows in set (0.00 sec)

mysql> select (select count(*) from user) = (select count(*) from (select distinct name from user) t);

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

| (select count(*) from user) = (select count(*) from (select distinct name from user) t) |

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

| 0 |

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

1 row in set (0.01 sec)

mysql> delete from user where id=5;

Query OK, 1 row affected (0.05 sec)

mysql> select * from user;

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

| id | name | address |

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

| 1 | aaa | beijing |

| 2 | bbb | shanghai |

| 3 | ccc | hangzhou |

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

3 rows in set (0.00 sec)

mysql> select (select count(*) from user) = (select count(*) from (select distinct name from user) t);

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

| (select count(*) from user) = (select count(*) from (select distinct name from user) t) |

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

| 1 |

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

1 row in set (0.00 sec)