SQL Server CASE WHEN in WHERE clause - sql-server

Question

I have a query with some joins. One of the joins depends of another value.
This is my query:
SELECT *
FROM CLIIRE A
LEFT JOIN CLIIOR B ON A.PTA = B.PTA AND A.ORD = B.ORD AND A.ITE = B.ITE
LEFT JOIN CLIORD C ON C.PTA = B.PTA AND C.ORD = B.ORD
LEFT JOIN CLIPAC D ON C.OPA = D.ORI AND C.PAC = D.PAC
LEFT JOIN CLIREN E ON E.NRE = A.NRE AND D.INS = E.INS AND A.CPT = E.CPT
LEFT JOIN
(SELECT *
FROM CLINOM
WHERE CLA = (CASE WHEN B.PFA = '88882' THEN 'MD' ELSE 'BU' END )) AS N ON B.PFA = N.COD
LEFT JOIN
(SELECT *
FROM CLIMED WHERE PRE = '') AS M ON B.PFA = M.MED
LEFT JOIN CLIPRF P ON B.PRF = P.PRF
WHERE
(D.INS LIKE 'OM%' OR D.INS LIKE 'SOL%')
AND E.NFA IN ('5188')
AND A.CPT IN ('fi', 'pi')
ORDER BY
E.NFA
But I'm getting error in the line:
LEFT JOIN (SELECT * FROM CLINOM WHERE CLA = (CASE WHEN B.PFA = '88882' THEN 'MD' ELSE 'BU' END )) AS N ON B.PFA=N.COD
Looks like SQL Server won't allow me to do that:
The multi-part identifier "B.PFA" could not be bound
The column B.PFA exists.
Can anyone help me? Thanks !

Answer 1

The problem is that the outer query reference is not available in the subquery. Happily, though the subquery is not needed. Try this logic:
LEFT JOIN CLINOM N
ON P.FA = N.COD AND
N.CLA = (CASE WHEN B.PFA = '88882' THEN 'MD' ELSE 'BU' END)
And, you can phrase this without the CASE. Assuming B.PFA is not NULL:
LEFT JOIN CLINOM N
ON P.FA = N.COD AND
((N.CLA = 'MD' AND B.PFA = '88882') OR
(N.CLA = 'BU' AND B.PFA <> '88882')
)
If B.PFA could be NULL:
LEFT JOIN CLINOM N
ON P.FA = N.COD AND
((N.CLA = 'MD' AND B.PFA = '88882') OR
(N.CLA = 'BU' AND (B.PFA <> '88882' OR B.PFS IS NULL))
)
You can also use COALESCE() if you like.