SQL : ISNULL in Join condition - sql

Question

Is there any other way to write this. If the Credit cardID in Application table is NULL, then join CreditcardID from Terminatedcreditcard table. Thanks,
This is the error:
Msg 4104, Level 16, State 1, Line 18
The multi-part identifier "TC.CreditCardID" could not be bound.
Code:
SELECT DISTINCT
prg.Title AS Program, a.Patientid,
a. Applicationid,
PT.MCC,
PT.MerchantName,
PT.MerchantCity, PT.MerchantState,
PT.MerchantZip,
PT.SettlementTransactionID,
CONVERT(DATE, PT.SettlementDate) AS SettlementDate
ABS(PT.Amount) as TransactionAmount
FROM
[dbo].[StagingSettlements] PT
LEFT JOIN
dbo.Application a ON PT.[CustomId] = ISNULL(a.CreditCardId, TC.CreditCardID)
LEFT JOIN
dbo.TerminatedCreditCard TC ON TC.ApplicationId = a.ApplicationId

Answer 1

You can change join precedence to get this:
FROM [dbo].[StagingSettlements] AS PT
LEFT JOIN ( dbo.Application AS a
LEFT JOIN dbo.TerminatedCreditCard AS TC on TC.ApplicationId = a.ApplicationId )
ON PT.[CustomId] = ISNULL( a.CreditCardId, TC.CreditCardID )
The addition of parentheses above causes Application to TerminatedCreditCard join to be evaluated first and the result is then joined to StagingSettlements.

Answer 2

A couple of points:
You don't appear to actually be using a credit card number in your result set, so I'm not clear on why you want it?
You need to put the NULL check in the join on TerminatedCreditCard. You are getting the error because you are trying to reference TerminatedCreditCard before you have joined to it.
The below SQL should sort you out, I wasn't sure of what the join condition would be between StagingSettlements and application, so I have just put in a placeholder which you will need to update, I have also added a 'CreditCardId' to the select:
SELECT Distinct
prg.Title as Program
,a.Patientid
,a.Applicationid
,PT.MCC
,PT.MerchantName
,PT.MerchantCity
,PT.MerchantState
,PT.MerchantZip
,PT.SettlementTransactionID
,convert(Date,PT.SettlementDate) as SettlementDate
,ABS(PT.Amount) as TransactionAmount
,COALESCE(TC.CreditCardId, a.CreditCardId) as CreditCardId
FROM [dbo].[StagingSettlements] PT
LEFT JOIN dbo.Application a
ON a.<applicationid> = PT.<applicationid>
LEFT JOIN dbo.TerminatedCreditCard TC
ON TC.ApplicationId = a.ApplicationId
AND a.CreditCardId IS NULL