Question

我有一张表“c31805”，看起来像这样：

| Id3| COL 1  |<br/>
|----|--------|<br/>
| 1  | trial1 |<br/>
| 2  | x142   |<br/>
| 3  | left   |<br/>
| 4  | left   |<br/>
| 5  | left   |<br/>
| 6  | trial2 |<br/>
| 7  | x139   |<br/>
| 8  | left   |<br/>
| 9  | left   |<br/>
| 10 | trial3 |<br/>
|----|--------|<br/>

有没有办法在这种情况下删除重复的“左”，它们是直接相互跟随的。但不是后来的那些。最终结果应如下所示：

| Id3| COL 1  |<br/>
|----|--------|<br/>
| 1  | trial1 |<br/>
| 2  | x142   |<br/>
| 3  | left   |<br/>
| 6  | trial2 |<br/>
| 7  | x139   |<br/>
| 8  | left   |<br/>
| 10 | trial3 |<br/>
|----|--------|<br/>

我尝试过选择来过滤重复项：

`SELECT `Id3` 
from c31805 a1 
where 0 < (select count(*) from c31805 a2 where a2.Id3 = a1.Id3 + 1 and a2.`COL 1` = a1.`COL 1`);

这似乎有效。

然后我尝试添加删除：

DELETE FROM c21705 
where id3 in (SELECT `Id3` from c21705 m1 where 0 < (select count(*) from c31805 m2 where m2.Id3 = m1.Id3 + 1 and m2.`COL 1` = m1.`COL 1`));

但是这会导致错误消息：

“＃1093 - 表'c21705'被指定两次，既作为'DELETE'的目标，也作为单独的数据来源”

有没有办法实现这个目标。

Answer 1

我认为您必须使用别名来避免混淆，

您的查询将如下所示。

DELETE `t` FROM c21705 as `t` where t.id3 in (SELECT Id3 from c21705 m1 where 0 < (select count(*) from c31805 m2 where m2.Id3 = m1.Id3 + 1 and m2.COL 1= m1.COL 1));

Answer 2

下面的查询将保留具有最低Id3值的重复值

DELETE FROM c31805
WHERE Id3 NOT IN (SELECT Id3 FROM t
                        ( SELECT [COL 1], MIN(Id3) as Id3
                          FROM c31805
                          GROUP BY [COL 1]
                          ) t

Mysql使用以下ID删除重复项

2 个答案: