SQL update from one Table to another based on a ID match IN db2

Question

The Query below is suited in SQL sErver. But in DB2 it does not give results:

Error is  SQLCODE = -199, ERROR:  ILLEGAL USE OF KEYWORD FROM. 

Answer 1

If you want to use UPDATE rather than MERGE, you want to process only the matching records where the value will change.

UPDATE Sales_Import SI
  SET SI.AccountNumber = 
        (SELECT RAN.AccountNumber
           FROM RetrieveAccountNumber RAN
           WHERE SI.LeadID = RAN.LeadID
           FETCH FIRST ROW ONLY
        )
  WHERE SI.LeadID IN
        (SELECT S2.LeadID
           FROM Sales_Import S2
           JOIN RetrieveAccountNumber R2
             ON S2.LeadID = R2.LeadID
           WHERE S2.AccountNumber <> R2.RetrieveAccountNumber 
        )