Question

I have a table that holds only two columns – a ListID and PersonID. When a person is merged with another in the system, I was to update all references from the ‘source’ person to be references to the ‘destination’ person.

Ideally, I would like to call something simple like

UPDATE MailingListSubscription SET PersonID = @DestPerson WHERE PersonID = @SourcePerson 

However, if the destination person already exists in this table with the same ListID as the source person, a duplicate entry will be made. How can I perform this action without creating duplicated entries? (ListID, PersonID is the primary key)

EDIT: Multiple ListIDs are used. If SourcePerson is assigned to ListIDs 1, 2, and 3, and DestinationPerson is assigned to ListIDs 3 and 4, then the end result needs to have four rows – DestinationPerson assigned to ListID 1, 2, 3, and 4.

Answer 1

--out with the bad DELETE FROM MailingListSubscription WHERE PersonId = @SourcePerson   and ListID in (SELECT ListID FROM MailingListSubscription WHERE PersonID = @DestPerson)  --update the rest (good) UPDATE MailingListSubscription SET PersonId = @DestPerson WHERE PersonId = @SourcePerson