SQL删除最早的记录表中​​的

Question

我正在寻找一个SQL查询到在Oracle表将保留在表中的记录n个，并删除运行，其余

我尝试以下

delete from myTable where pk not in 
(SELECT pk FROM myTable where rownum <5 order by created DESC) 

但现在看来，我不能在嵌套选择order by。

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Answer 1

当您使用ORDER BY与ROWNUM的ROWNUM首先应用，这样你就不会得到你所期望的结果。你可以修改你的SQL：

delete from myTable where pk not in 
(SELECT pk FROM 
    (SELECT pk FROM myTable order by created DESC) 
    where rownum <5 
) 

还有很多其他的方法来写这个。如果桌子很大，大部分的行都会被删除，那么这可能会更快：

delete from myTable where created < 
(SELECT MIN(created) FROM 
    (SELECT created FROM myTable order by created DESC) 
    where rownum <5 
)