Single-row subquery returns more than one row - Case statement - sql

Question

My following code returns the error stated in the title, however the error does not show when the case statement is ran by itself.
I've tried to dismantle the case statement, however this isn't my query but IS being used elsewhere, i'm wondering how they manage to get it to return rows in its current state.
SELECT DISTINCT V55."INPUTSPECNAME",
V55."FKMATERIAL",
V55."INPUTQUANTITYVALUE",
B.ABBREVIATION,
(CASE
WHEN z.COST IS NULL
THEN (SELECT DISTINCT (CASE
WHEN MatOut_D.PERVALUEQUANTITY > 0 THEN
ROUND(MatOut_D.PRICE /
MatOut_D.PERVALUEQUANTITY /
10 /
MatOut_E.USDCONVERSIONFACTOR *
C.USDCONVERSIONFACTOR, 5)
ELSE 0
END)
FROM V55_FORMULATIONJOINMATOUTPUT MatOut_B,
V55_FORMULATIONINPUTOUTPUT MatOut_C,
THEORETICALCOSTS MatOut_D,
COMMONCURRENCIES MatOut_E,
UOMML MatOut_F
WHERE MatOut_B.FKREFERENCEDMATERIAL = V55.FKMATERIAL
AND MatOut_B.FKOWNER = MatOut_C.FKOWNER
AND MatOut_C.FORMULATIONOUTPUTPKID = MatOut_D.FKPARENT
AND MatOut_D.FKCURRENCY = MatOut_E.PKID
AND MatOut_D.FKPERVALUEUOM = MatOut_F.FKUOM
AND MatOut_F.LANGID = 0)
ELSE ROUND(z.COST*100/D.USDCONVERSIONFACTOR*C.USDCONVERSIONFACTOR,5)
END) AS COST_100G
FROM V55_FORMULATIONINPUTOUTPUT V55
INNER JOIN UOM A
on V55.FKINPUTUOM = A.PKID
INNER JOIN UOMML B
on a.pkid = B.FKUOM
INNER JOIN DWBSpecificationRoots dwbRoot
on dwbRoot.fkOwner = V55.FKOWNER
INNER JOIN dwbSpecifications dwbSpec
ON dwbSpec.fkWorkingVersionParent = dwbRoot.pkid
LEFT OUTER JOIN specLegacySpecJoin y
on dwbSpec.fkdisplayedlegacyprofile = y.fklegacyprofileid
and y.fkspecid = V55.fkMaterial
LEFT OUTER join COSTITEMS z
on z.equivalent = y.equivalent
and z.fklegacyprofile = dwbSpec.fkdisplayedlegacyprofile
and z.FKSCRMENTITY = dwbSpec.FKSCRMSUPPLIERBASE
and z.COSTTYPE = dwbSpec.COSTTYPE
LEFT OUTER JOIN COMMONCURRENCIES C
ON C.PKID = dwbSpec.FKCURRENCY
LEFT OUTER JOIN COMMONCURRENCIES D
ON D.PKID = Z.FKCURRENCY

Answer 1

The problem is that the subquery in your CASE statement is returning multiple rows in some situations and as has been stated in the question's comments that's a no-no.
I suggest that you pull the subquery out of the CASE statement and make it a Common Table Expression, then join it into the query as you would any other table:
WITH cteSubexpr AS (SELECT DISTINCT MatOut_B.FKREFERENCEDMATERIAL,
(CASE
WHEN MatOut_D.PERVALUEQUANTITY > 0 THEN
ROUND(MatOut_D.PRICE /
MatOut_D.PERVALUEQUANTITY /
10 /
MatOut_E.USDCONVERSIONFACTOR *
C.USDCONVERSIONFACTOR, 5)
ELSE 0
END) AS CALC_QTY
FROM V55_FORMULATIONJOINMATOUTPUT MatOut_B
INNER JOIN V55_FORMULATIONINPUTOUTPUT MatOut_C
ON MatOut_C.FKOWNER = MatOut_B.FKOWNER
INNER JOIN THEORETICALCOSTS MatOut_D
ON MatOut_D.FKPARENT = MatOut_C.FORMULATIONOUTPUTPKID
INNER JOIN COMMONCURRENCIES MatOut_E
ON MatOut_E.PKID = MatOut_D.FKCURRENCY
INNER JOIN UOMML MatOut_F
ON MatOut_F.FKUOM = MatOut_D.FKPERVALUEUOM
WHERE MatOut_F.LANGID = 0)
SELECT DISTINCT V55.INPUTSPECNAME,
V55.FKMATERIAL,
V55.INPUTQUANTITYVALUE,
B.ABBREVIATION,
(CASE
WHEN z.COST IS NULL
THEN cs.CALC_QTY
ELSE ROUND(z.COST * 100 / D.USDCONVERSIONFACTOR * C.USDCONVERSIONFACTOR, 5)
END) AS COST_100G
FROM V55_FORMULATIONINPUTOUTPUT V55
INNER JOIN cteSubexpr cs
ON cs.FKREFERENCEDMATERIAL = V55.FKMATERIAL
INNER JOIN UOM A
on V55.FKINPUTUOM = A.PKID
INNER JOIN UOMML B
on a.pkid = B.FKUOM
INNER JOIN DWBSpecificationRoots dwbRoot
on dwbRoot.fkOwner = V55.FKOWNER
INNER JOIN dwbSpecifications dwbSpec
ON dwbSpec.fkWorkingVersionParent = dwbRoot.pkid
LEFT OUTER JOIN specLegacySpecJoin y
on dwbSpec.fkdisplayedlegacyprofile = y.fklegacyprofileid
and y.fkspecid = V55.fkMaterial
LEFT OUTER join COSTITEMS z
on z.equivalent = y.equivalent
and z.fklegacyprofile = dwbSpec.fkdisplayedlegacyprofile
and z.FKSCRMENTITY = dwbSpec.FKSCRMSUPPLIERBASE
and z.COSTTYPE = dwbSpec.COSTTYPE
LEFT OUTER JOIN COMMONCURRENCIES C
ON C.PKID = dwbSpec.FKCURRENCY
LEFT OUTER JOIN COMMONCURRENCIES D
ON D.PKID = Z.FKCURRENCY
Best of luck.