tsql - Group By on computed columns - tsql

Question

Please advice on a better way to do this.
I am sure this can be done in one query itself.
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

obvious change is to use sub-queries:
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
but you don't group on computed columns, so you can go with simple one:
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