na tvoe mesto ne bich experimentirala s triger ako ne si savsem siguren kakvo pravich, verojatnosta da si modelirach dannite e goljama, no ako naistina te interesuva eto primer kak se programira:

INSTEAD OF INSERT
++++++++++++++++++++
CREATE TRIGGER trgi_i_tab1 ON tab1 INSTEAD OF INSERT
AS
IF @@ROWCOUNT = 0 RETURN
INSERT INTO tab1(city, state, zip, <other columns>)
SELECT ISNULL(city, ''), ISNULL(state, ''), ISNULL(zip, '00000'), <other
columns>
FROM inserted // ili vmesto gornia select

if EXISTS(SELECT * FROM dbo.tabl INNER JOIN inserted
ON dbo.tab1.city= inserted.city)