Question

declare  @userid int
set @userid=9846
SELECT TOP 10 
          tagid, 
          [Description]
FROM   tagsuggestion 
WHERE  tagid IN (SELECT **DISTINCT** TOP 10  tagid
             FROM  (SELECT ulpt.tagid, 
                           createddate 
                    FROM   userlocationposttag ulpt 
                            WHERE  ulpt.UserID=@userid                                

                    UNION ALL 
                    SELECT ult.tagid, 
                           createddate 
                    FROM   userlocationtag ult 
                             WHERE  ult.UserID=@userid
                    UNION ALL 
                    SELECT upt.tagid, 
                           createddate 
                    FROM   userprofiletag upt 
                             WHERE  upt.UserID=@userid
) T

             ORDER  BY createddate DESC)  

The above query is error ORDER BY items must appear in the select list if SELECT DISTINCT is specified.

.but if i remove DISTINCT this query runs

I want to ensure the distinctness and i also want to keep the sort order by createddate DESC

one of my associated post is

Last created 10 records from all of the 3 tables

Answer 1

Okay, so we only care about each tag based on it’s most recent created date, so we can structure the inner query as:

SELECT tagid,MAX(createddate) as createddate FROM (
SELECT ulpt.tagid, 
       createddate 
FROM   userlocationposttag ulpt 
WHERE  ulpt.UserID=@userid                                
UNION ALL 
SELECT ult.tagid, 
       createddate 
FROM   userlocationtag ult 
WHERE  ult.UserID=@userid
UNION ALL 
SELECT upt.tagid, 
       createddate 
FROM   userprofiletag upt 
WHERE  upt.UserID=@userid
) t
GROUP BY tagid

And then we can wrap that in another subselect, and apply the top ten:

SELECT TOP 10 tagid FROM (
SELECT tagid,MAX(createddate) as createddate FROM (
SELECT ulpt.tagid, 
       createddate 
FROM   userlocationposttag ulpt 
WHERE  ulpt.UserID=@userid                                
UNION ALL 
SELECT ult.tagid, 
       createddate 
FROM   userlocationtag ult 
WHERE  ult.UserID=@userid
UNION ALL 
SELECT upt.tagid, 
       createddate 
FROM   userprofiletag upt 
WHERE  upt.UserID=@userid
) t
GROUP BY tagid
) t ORDER BY createddate desc

And we no longer need distinct (because GROUP BY and MAX already ensured that each tag only appears once)