Questsion about using HAVING in ACCESS SQL - sql

Question

I wanted to get clarity on how the HAVING component in an SQL statement works, particularly with a SQL statement that has multiple joins. Consider the following SQL select statement:
SELECT
p.id,
p.first_name as [First Name],
p.last_name as [Last Name]
FROM
( [tbl_person] as p
INNER JOIN [tbl_person_languages] as pl
ON [p].[id] = [pl].[person_id])
INNER JOIN [tbl_person_crossCuttingSkills] As ccp
ON [p].[id] = [ccp].[person_id]
WHERE
cint(pl.language_id) in (12,14) AND
cint(ccp.skill_id) in (55)
GROUP BY
p.id,
p.first_name,
p.last_name
HAVING
count(pl.language_id) =2 AND
count(ccp.skill_id) = 1
I want to pull out records, from tbl_person, where a record has all of the WHERE requirements. For example: I want to select all users where they speak a languages Italian (with ID 12) and Spanish (ID 15) AND have a skill of cooking (55). They need to have all requirements, not just one or more. I was under the assumption this is where you would use GROUP BY and HAVING. With the HAVING:
count(pl.language_id) =2
I use count = 2 because there are two options in the language WHERE clause (12 and 14)
And I use
count(ccp.skill_id) = 1
Because there is one value in the WHERE clause (55).
Is this the correct way to be doing this? For some reason, this returns no records (I have one record in my DB of a person who fits these requirements exactly). But, if I change my HAVING to:
count(pl.language_id) =2 AND
count(ccp.skill_id) = 2
It works fine. Why is this? Are my assumptions of how this works incorrect or is there something else going on?

Answer 1

Remember what count() does . . . it counts non-NULL values. So, you are counting two non-NULL values then the counts are the same.
In most dialects of SQL, you can fix this by doing:
HAVING count(distinct pl.language_id) = 2 AND count(distinct ccp.skill_id) = 1
But that doesn't work in MS Access, because MS Access does not support COUNT(DISTINCT).
So, you can be more verbose. In your case:
HAVING SUM(iif(cint(pl.language_id) = 12, 1, 0)) > 0 AND
SUM(iif(cint(pl.language_id) = 14, 1, 0)) > 0 AND
SUM(iif(cint(ccp.skill_id) = 55, 1, 0)) > 0
I'm sorry this HAVING clause is not simpler. You could switch to another database (such as SQL Server Express) that more closely aligns with ANSI functionality.