Question

我在页面上有一个内容表。该页面分为几个部分。我想获得每个页面部分的最新版本。

Id（int）版本（int） SectionID

Id    Version    SectionID    Content
1       1           1           AAA
2       2           1           BBB
3       1           2           CCC
4       2           2           DDD
5       3           2           EEE

我想得到：

Id    Version    SectionID    Content
2       2           1           BBB
5       3           2           EEE

Answer 1

您可以使用独家自助加入：

select  last.*
from    YourTable last
left join
        YourTable new
on      new.SectionID = last.SectionID
        and new.Version > last.Version
where   new.Id is null

where语句基本上表示：此行没有更新版本。

稍微更具可读性，但通常更慢，是not exists条件：

select  *
from    YourTable yt
where   not exists
        (
        select  *
        from    YourTable yt2
        where   yt2.SectionID = yt.SectionID
                and yt2.Version > yt.Version
        )

Answer 2

示例表定义：

declare @t table(Id int, [Version] int, [SectionID] int, Content varchar(50))

insert into @t values (1,1,1,'AAA');
insert into @t values (2,2,1,'BBB');
insert into @t values (3,1,2,'CCC');
insert into @t values (4,2,2,'DDD');
insert into @t values (5,3,2,'EEE');

工作解决方案：

select A.Id, A.[Version], A.SectionID, A.Content
from @t as A
join (
    select max(C.[Version]) [Version], C.SectionID
    from @t C
    group by C.SectionID
) as B on A.[Version] = B.[Version] and A.SectionID = B.SectionID
order by A.SectionID

Answer 3

更简单，更易读的解决方案：

select A.Id, A.[Version], A.SectionID, A.Content
from @t as A
where A.[Version] = (
    select max(B.[Version])
    from @t B
    where A.SectionID = B.SectionID
)

Answer 4

我刚看到Oracle有一个very similar question，根据性能确定了答案。

也许如果你的表很大，性能是一个问题你可以尝试看看SQL服务器是否也表现更好：

select Id, Version, SectionID, Content
from (
    select Id, Version, SectionID, Content,
           max(Version) over (partition by SectionID) max_Version
    from   @t
) A
where Version = max_Version

获取分组依据的最大列

4 个答案: