mysql - DELETE FROM 抛出 SQL 错误 [1064] [42000] : (conn=5159) on a query,，而 SELECT 在该错误上

Question

尝试在 MySQL 查询中删除特定数量的行，我可以使用以下命令SELECT我想要删除的任何内容，获得我需要的结果:

select * from ns_cos ns where ns.created_at <>
    (select max(nsa.created_at) from ns_cos nsa
        where nsa.month_year = ns.month_year)

但是，当我尝试使用以下方法删除所选数据时:

delete from ns_cos ns where ns.created_at not exists
    (select max(nsa.created_at) from ns_cos nsa
        where nsa.month_year = ns.month_year)

我得到:

SQL Error [1064] [42000]: (conn=5159) You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near 'ns where ns.created_at not exists (select max(nsa.created_at) from ns_cos nsa wh' at line 1

我做错了什么？

Answer 1

您面临的直接问题是，并非所有 MySQL 版本都支持直接在 delete from 中为表添加别名。此外，您无法重新打开在 from 子句中删除 from 的表。

考虑使用delete ... join语法。

delete ns
from ns_cos ns
inner join (
    select month_year, max(nsa.created_at) created_at
    from ns_cos nsa 
    group by month_year
) ns1 on ns1.month_year = ns.month_year and ns1.created_at <> ns.created_at