mysql中You can't specify target table for update in FROM clause错误

最新推荐文章于 2024-07-25 11:42:08 发布

转载最新推荐文章于 2024-07-25 11:42:08 发布 · 94 阅读

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原文链接：http://blog.51cto.com/5317968/1674066

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#数据库

本文详细解释了MySQL中'You can't specify target table for update in FROM clause'错误的原因，并提供了一个实例演示如何避免该问题。通过将查询结果再次通过中间表选择一遍，可以解决在单个SQL语句中同时进行选择和更新操作导致的问题。

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mysql中You can't specify target table <tbl> for update in FROM clause错误的意思是说，不能先select出同一表中的某些值，再update这个表(在同一语句中)。例如下面这个sql：

delete from tbl where id in
(
       select max(id) from tbl a where EXISTS
       (
           select 1 from tbl b where a.tac=b.tac group by tac HAVING count(1)>1
       )
       group by tac
)

改写成下面就行了：

delete from tbl where id in
(
   select a.id from
   (
       select max(id) id from tbl a where EXISTS
       (
           select 1 from tbl b where a.tac=b.tac group by tac HAVING count(1)>1
       )
       group by tac
   ) a
)

也就是说将select出的结果再通过中间表select一遍，这样就规避了错误。注意，这个问题只出现于mysql，mssql和oracle不会出现此问题。

例子：

delete from brand

where brand_store_sn in(

select a.brand_store_sn from (select brand_store_sn from brand

group by brand_store_sn

HAVING COUNT(brand_store_sn)>1) a

)

and id not in (

select a.id from (select max(id) as id from brand

group by brand_store_sn

HAVING COUNT(brand_store_sn)>1) a