T-SQL Aggregate function subquery - sql-server

Question

I get the following error:
Cannot perform an aggregate function on an expression containing an aggregate or a subquery.
With this code:
SELECT
loc.Location
,COUNT(CASE
WHEN hr.SAC in (SELECT [SAC] FROM dbo.[Titles] WHERE [title] = 'XYZ')
THEN 1
ELSE NULL
END) AS XYZ_Trainee_Count
,COUNT(CASE
WHEN hr.SAC in (SELECT [SAC] FROM dbo.[Titles] WHERE [title] = 'ABC')
THEN 1
ELSE NULL
END) AS ABC_Trainee_Count
FROM
dbo.n_HRODS hr INNER JOIN dbo.Locations loc
ON loc.LocationID = hr.LocationID
INNER JOIN dbo.EmpData dat
ON dat.EmpID = hr.EmpID
WHERE dat.Trainee = 1
GROUP BY loc.Location
dbo.[Titles] is a view that combines two columns from two other tables. I'm basically doing it this way because the programmer before me did something like this:
,COUNT(CASE
WHEN SAC in ( lists about 30 items)
THEN 1
ELSE NULL
END)
Obviously, I don't want to list 30 items in that case statement... and when those items change for whatever reason in 3 years, then who's going to remember to go back in this code and updated those items? Nobody...
Thanks in advance for your help.

Answer 1

You can do this with a couple of extra LEFT OUTER JOINs to that title table:
SELECT
loc.Location
,COUNT(CASE WHEN titles1.[SAC] IS NOT NULL THEN 1 ELSE NULL END) AS XYZ_Trainee_Count
,COUNT(CASE WHEN titles2.[SAC] IS NOT NULL THEN 1 ELSE NULL END) AS ABC_Trainee_Count
FROM
dbo.n_HRODS hr INNER JOIN dbo.Locations loc
ON loc.LocationID = hr.LocationID
INNER JOIN dbo.EmpData dat
ON dat.EmpID = hr.EmpID
LEFT OUTER JOIN dbo.[Titles] titles1
ON titles1.[title]='XYZ' AND
hr.SAC = titles1.[SAC]
LEFT OUTER JOIN dbo.[Titles] titles2
ON titles2.[title]='ABC' AND
hr.sac = titles2.[SAC]
WHERE dat.Trainee = 1
GROUP BY loc.Location
Alternatively, if you are really married to those subqueries in your SELECT statement because the actual query is a big nightmare and the thought of monkeying with the joins is enough to make you faint, then you can just remove the aggregation from this query and shove it all into a subquery before aggregation:
SELECT location, count(XYZ_Trainee) AS XYZ_Trainee_Count, count(ABC_Trainee) as ABC_Trainee
FROM
(
SELECT
loc.Location
,CASE
WHEN hr.SAC in (SELECT [SAC] FROM dbo.[Titles] WHERE [title] = 'XYZ')
THEN 1
ELSE NULL
END AS XYZ_Trainee
,CASE
WHEN hr.SAC in (SELECT [SAC] FROM dbo.[Titles] WHERE [title] = 'ABC')
THEN 1
ELSE NULL
END AS ABC_Trainee
FROM
dbo.n_HRODS hr INNER JOIN dbo.Locations loc
ON loc.LocationID = hr.LocationID
INNER JOIN dbo.EmpData dat
ON dat.EmpID = hr.EmpID
WHERE dat.Trainee = 1
) sub
GROUP BY location
I would aim for the first solution though since it's going to be easier to maintain and probably get a better execution path from your RDBMS and run quicker as a result. Although... that's just a guess.

Answer 2

Very similar to JNevill first answer. But if you join with title once, you can check and count for any number of title you want.
SELECT
loc.Location
,COUNT(CASE WHEN t.[title] = 'XYZ' THEN 1 END) AS XYZ_Trainee_Count
,COUNT(CASE WHEN t.[title] = 'ABC' THEN 1 END) AS ABC_Trainee_Count
FROM
dbo.[n_HRODS] hr
INNER JOIN dbo.[Locations] loc
ON loc.LocationID = hr.LocationID
INNER JOIN dbo.[EmpData] dat
ON dat.EmpID = hr.EmpID
INNER JOIN dbo.[Titles] t
ON hr.SAC = t.[SAC]
WHERE dat.Trainee = 1
GROUP BY loc.Location