mysql - 如何使用字段的最大值编写更新查询？

Question

我想执行此查询，但出现错误。我怎样才能运行这种类型的查询？

UPDATE `user` 
SET id = (SELECT (MAX(t.id)+1) as id FROM `user` as t)
WHERE id='';

错误信息是:

[SQL]UPDATE `user`  SET id = (SELECT (MAX(t.id)+1) as id FROM `user` as t) WHERE id='' LIMIT 1; 
[Err] 1093 - You can't specify target table 'user' for update in FROM clause

我的表场景是

--------------
|User        |
--------------
| id  | name |
--------------
| 101 | A    |
--------------
|     | B    |
--------------
|     | C    |
--------------
|     | D    |
--------------

我想这样更新

--------------
|User        |
--------------
| id  | name |
--------------
| 101 | A    |
--------------
| 102 | B    |
--------------
| 103 | C    |
--------------
| 104 | D    |
--------------

Answer 1

您可以使用变量来实现您的需要。

set @rownum:=101;
update user set id = @rownum:=@rownum+1 where id is null

Check Demo Here