LEFT OUTER JOIN Information_Sales A ON Case IF EID = 0 or PID = 0 then SID = 148 ELSE UDF.NEW (EID,PID) = A.SID

Its important to remember that a CASE expression is an expression, which produces a single scalar value. It is not an IF clause.

Assuming that the SID = 148 and A.Sid are the same column. You want something more like this

LEFT OUTER JOIN Information_Sales A on A.SID = Case When EID = 0 then 148 when PID = 0 then 148 else UDF.NEW (EID,PID) end

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Note: NO guarantees on performance of such a join. You may well be better off doing separate queries

LEFT OUTER JOIN Information_Sales A on SID = 148

WHERE EID = 0 or PID = 0

LEFT OUTER JOIN Information_Sales A on UDF.NEW (EID,PID)

WHERE EID <> 0 and PID <> 0

As has already been pointed out. A lot more information is needed before anyone can give you solid, specific advice.