Defensive Database Programming - Red Gate Software

Chapter 6: Common Problems with Data Integrity(snip)ItemLabel OldBarcode NewBarcode--------------- -------------------- --------------------Flashlight 234567 2345679Lamp 123457 1234579Listing 6-50: Our altered trigger properly handles multi-row updates.The first lesson here is that, when developing triggers, the defensive programmer shouldalways use proper set-based logic, rather than iterative logic.Mishandling updates that affect the primary keyWe have fixed one problem in our trigger, but it has another serious bug; it doesnot handle the case when the primary key column is also modified. Listing 6-51demonstrates the problem. This time, the code also updates the ItemLabel column,which forms part of our Primary Key, as well as the Barcode column.BEGIN TRAN ;DELETE FROM dbo.ItemBarcodeChangeLog ;UPDATE dbo.ItemsSET ItemLabel = ItemLabel + 'C' ,Barcode = Barcode + '9' ;SELECT ItemLabel ,OldBarcode ,NewBarcodeFROM dbo.ItemBarcodeChangeLog ;ROLLBACK ;debugging output: data before updateItemLabelBarcode------------------------------ ---------------------------Lamp 123457200