sql server 是否介意记录插入的方式? [英] Does sql server minds the way records where inserted?

问题描述

(它是如何工作的" - 问题)

假设我有这张表:

   Id            val
    ------------------
    1             a       <--
    1             a
    1             a
    2             b       <--
    2             b
    2             b

现在假设我想要标记的行:

Now lets say I want the marked rows :

我可以依靠这个查询吗:

Can I count on this query :

select id,val from (
select id , val , row_number() over (partition by id order by id) as rn
) k where rn=1

给我 Selected 行?

(注意 order by 子句).它会认为顺序是插入的顺序吗?

(notice the order by clause). will it consider the order as the order they were inserted ?

推荐答案

不保证行为.您的查询将返回两行，但未定义哪一行.

The behaviour is not guaranteed. Your query will return two rows, but which ones is undefined.

当我尝试

create table #t (id int, val char(1), t timestamp)
insert #t  (id, val) values (1,'a')
insert #t  (id, val) values (1,'a')
insert #t  (id, val) values (2,'b')

insert #t  (id, val) values (1,'a')
insert #t  (id, val) values (2,'b')
insert #t  (id, val) values (2,'b')
select * from #t 

select * from ( 
select *, row_number() over (partition by id order by id) as rn from #t  
) k where rn=1 


drop table #t

结果是可变的，取决于插入的顺序，但不是一致的第一个插入的行.

the results are variable, depending on the order of insertion, but not consistently the first inserted rows.

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