I have a database with account numbers and card numbers. I match these to a file to update any card numbers to the account number, so
I believe an UPDATE FROM with a JOIN will help:
UPDATE
Sales_Import
SET
Sales_Import.AccountNumber = RAN.AccountNumber
FROM
Sales_Import SI
INNER JOIN
RetrieveAccountNumber RAN
ON
SI.LeadID = RAN.LeadID;
UPDATE
Sales_Import SI,
RetrieveAccountNumber RAN
SET
SI.AccountNumber = RAN.AccountNumber
WHERE
SI.LeadID = RAN.LeadID;