CREATE TRIGGER Table_A_Update ON itensNota FOR INSERT
AS
DECLARE @IDPAI VARCHAR(200), @IDNOTA VARCHAR(200);
BEGIN
    SELECT @IDPAI = i.idPai FROM inserted i;
    SELECT @IDNOTA = i.idNota FROM inserted i;
    IF ( @idPai = 0 )
        UPDATE itensNota
        SET idPai = ( SELECT id FROM nota WHERE idNota = @IDNOTA )
        FROM itensNota a
        JOIN inserted i ON a.ID = i.ID AND a.idNota = i.idNota
END