mysql 的delete from 和update子查询限制

Posted 2021-01-19 O天国O

最经做项目时发现的问题，好像在update时也有。。。

 

网上查到的资料如下：

 

1.使用mysql进行delete from操作时，若子查询的 FROM 字句和更新/删除对象使用同一张表，会出现错误。 

mysql> DELETE FROM tab1 WHERE col1 = ( SELECT MAX( col1 ) FROM tab1 ); 
ERROR 1093 (HY000): You can’t specify target table ‘tab1′ for update in FROM clause 

针对“同一张表”这个限制，撇开效率不谈，多数情况下都可以通过多加一层select 别名表来变通解决，像这样 

DELETE FROM tab1 
WHERE col1 = ( 
SELECT MAX( col1 ) 
FROM ( 
SELECT * FROM tab1 
) AS t 
); 
或这样

delete from theTable where id in
(
select id from
(
select min(id) id from theTable group by title HAVING count(*)>1
) ids
) ;

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2. mysql delete from where in 时后面 的查询语句里不能加where条件 


Sql代码 
      delete from `t_goods` where fi_id in (select * from ( select fi_id from `t_goods` where fs_num is null and fs_name is null and fs_type is null and fs_using is null and fs_lifetime is null) b)  


Sql代码 
      delete from `t_goods` where fi_id in (select fi_id from `t_goods` where fs_num is null and fs_name is null and fs_type is null and fs_using is null and fs_lifetime is null)   


Sql代码 
      delete from `t_goods` where fi_id in ( select fi_id from `t_goods` )   

上面三种情况，只有中间的不能执行。 

综合起来就是mysql delete from where in 时后面 的查询语句里不能加where条件 

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3. delete from table... 这其中table不能使用别名 

Sql代码 

    delete from student a where a.id in (1,2);(执行失败) 

    

     select a.* from student a where a.id in (1,2);(执行成功)