Question

请建议更好的方法来做到这一点。我确信这可以在一个查询中完成。

declare @tempTale table (ID bigint, ArticleDate datetime,CommentDate 
datetime,MostRecentDate datetime) 

declare @MinDate datetime;
set @MinDate = getdate();
set @MinDate = DATEADD(YEAR,-100,@MinDate)

insert into @tempTale    
select USER_ARTICLEID, User_Article.CREATED_ON, coalesce(comment.CREATED_ON,@MinDate),
case when coalesce(User_Article.CREATED_ON,@MinDate) > coalesce(comment.CREATED_ON,@MinDate) then User_Article.CREATED_ON else comment.CREATED_ON end as MostRecentDate 
 from User_Article left join Comment on Comment.CONTENTID = User_Article.USER_ARTICLEID and comment.CONTENT_TYPE = User_Article.CONTENT_TYPE
 order by MostRecentDate desc

 select distinct top 10 ID,MAX(MostRecentDate) from @tempTale group by ID
 order by MAX(MostRecentDate) desc

Answer 1

明显的变化是使用子查询：

select distinct top 10 ID, MAX(MostRecentDate) from
(
select
    USER_ARTICLEID as ID,
    (case
        when coalesce(User_Article.CREATED_ON,@MinDate) > coalesce(comment.CREATED_ON,@MinDate) then User_Article.CREATED_ON
        else comment.CREATED_ON end) as MostRecentDate
from User_Article
left join Comment
on Comment.CONTENTID = User_Article.USER_ARTICLEID and comment.CONTENT_TYPE = User_Article.CONTENT_TYPE
)
group by ID
order by 2 desc

但您没有对计算列进行分组，因此您可以使用简单的列：

select distinct top 10
    USER_ARTICLEID as ID,
    (case
        when coalesce(User_Article.CREATED_ON,@MinDate) > coalesce(comment.CREATED_ON,@MinDate) then User_Article.CREATED_ON
        else comment.CREATED_ON end) as MostRecentDate
from User_Article
left join Comment
on Comment.CONTENTID = User_Article.USER_ARTICLEID and comment.CONTENT_TYPE = User_Article.CONTENT_TYPE
group by USER_ARTICLEID
order by 2 desc

tsql - 计算列上的分组依据

1 个答案: