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Example: Row Level Trigger
CREATE TRIGGER    NoLowerPrices
AFTER UPDATE OF  price  ON Product
REFERENCING
     OLD  AS OldTuple
     NEW  AS  NewTuple
WHEN (OldTuple.price > NewTuple.price)
     UPDATE  Product
     SET  price = OldTuple.price
     WHERE  name = NewTuple.name
FOR EACH ROW