Question

I have a SQL Query :

  SELECT * FROM Customer c
  LEFT JOIN  Invoice I ON  I.InvcNum = C.Cust_InvcNum

some thing changed and the join does not work because there is no consistency in the data in the ‘Cust_InvcNum’. So now when it does not find the record for the join or if it is null it needs to check for another condition.

 LEFT JOIN Invoice I ON I.InvcNum = (SELECT p.InvcPrefix FROM Prefix WHERE p.DealerID = I.DealrID )  + '-' + I.InvcNum

second join I do works but it is taking too long for it get me data. Is there any other way to do this.

Earlier it used to be

Join on I.InvcNum = C.Cust_InvcNum
both the columns has the same data like DlrCd-InvcNum i.e both the columns 1234-A789
but not it could match on the above data or now the column ‘InvcNum’ in invoice table
can be populated like Dlrd-InvcNum or InvcPrefix-InvcNum

So InvcNum = 1234-A789 but CustNum = I94-A789
so we need to check if the for InvoicePrefix-InvcNum

Answer 1

SELECT *
FROM Customer c 
  LEFT JOIN (
             SELECT i.InvcNum, p.InvcPrefix + '-' + I.InvcNum AS pInvcNum 
             FROM Invoice i LEFT JOIN Prefix p ON i.DealrID = p.DealrID
             ) ip ON c.Cust_InvcNum = CASE WHEN c.Cust_InvcNum = ip.InvcNum 
                                           THEN ip.InvcNum 
                                           ELSE ip.pInvcNum END