Disparador que registre unica vez

[Libras]

con triggers:

Código SQL:

CREATE TRIGGER dis_registro
ON empleado
FOR INSERT
AS
BEGIN
DECLARE @id INT
 
SELECT @id=id FROM inserted
 
IF(SELECT COUNT(*) FROM empleados  WHERE id=@)=0
    print 'Inserta'
ELSE
BEGIN
    print 'no inserta'
    ROLLBACK TRANSACTION
    RETURN;
END
END