Question

如何在mysql数据库中删除此表中的行，删除后我应该在列valeurs中有4个不同的值。

我的数据库的实际状态：

+----+-----------+---------+---------------------+
| id | action_id | valeurs | temps_action        |
+----+-----------+---------+---------------------+
| 81 |         1 | ON_1    | 2016-04-26 11:14:43 |
| 80 |         2 | OFF_2   | 2016-04-26 11:14:41 |
| 84 |         2 | OFF_2   | 2016-04-26 11:14:48 |
| 83 |         1 | ON_1    | 2016-04-26 11:14:46 |
| 79 |         1 | OFF_1   | 2016-04-26 11:14:40 |
| 78 |         2 | ON_2    | 2016-04-26 11:14:38 |
| 77 |         1 | ON_1    | 2016-04-26 11:14:35 |
| 82 |         2 | OFF_2   | 2016-04-26 11:14:45 |
+----+-----------+---------+---------------------+

我想最终：

+----+-----------+---------+---------------------+
| id | action_id | valeurs | temps_action        |
+----+-----------+---------+---------------------+
| 81 |         1 | ON_1    | 2016-04-26 11:14:43 |
| 80 |         2 | OFF_2   | 2016-04-26 11:14:41 |
| 79 |         1 | OFF_1   | 2016-04-26 11:14:40 |
| 78 |         2 | ON_2    | 2016-04-26 11:14:38 |
+----+-----------+---------+---------------------+

Answer 1

你可以这样使用

delete from   my_table  as t
where (t.id, t.valeurs) not  in ( select max(t2.id), t2.valeurs 
                            from my_table as t2
                             group by valeurs);

Answer 2

这样的查询为每个action_id，valeurs

保存了最多temps_action的行

delete 
    from  my_table 
  where (action_id, temps_action, valeurs) not in 
      (select * from (select action_id, max(temps_action), valeurs 
             from my_table 
          group by action_id, valeurs) t1);

Answer 3

您真正想要做的是删除重复的行。这是一个可以帮助您的示例查询：

DELETE FROM TableName  
WHERE valeurs IN (SELECT * 
             FROM (SELECT valeurs FROM TableName 
                   GROUP BY valeurs
 HAVING (COUNT(*) > 1) AS Something
                  ) 
            );

用condtion从mysql中删除

3 个答案: