Question

I want to push all data from SourceTable to TargetTable by inserting or updating accordingly. I don’t need any entries removing from TargetTable, even if they are not present in SourceTable.

This is what I have so far. Is the MERGE command the most suitable approach for this? I’ve had a look at some example but not quite sure on how to go about this.

My current solution truncates the whole table and then inserts of the data. I have since realised I need to keep the PK values for values that existed previously in the TargetTable. How do I change this to INsert or update depending on whether AssociatedRefId exists in the PublicRefId column of the TargetTable?

-- Truncate lancrm01sql's Baseline Official table
        TRUNCATE TABLE [TargetTable]

        -- Populate table
        INSERT INTO [TargetTable] 
        (PublicRefId 
        ,FamilyName 
        ,GivenName
        )
        SELECT 
            AssociatedRefId 
        ,   lastname 
        ,   firstname 

        FROM 
            #TempSourceTable

Answer 1

MERGE TargetTable AS T
USING #TempSourceTable AS S
ON (t.PublicRefId =  s.AssociatedRefId)
WHEN NOT MATCHED BY TARGET
    THEN INSERT(PublicRefId, FamilyName, GivenName) VALUES (S.AssociatedRefId, S.lastname, S.firstname)
WHEN MATCHED 
    THEN UPDATE SET T.FamilyName = S.lastname, T.GivenName = S.firstName

This article gives a pretty good explanation on using MERGE.