求大佬解答一下哪错了 ，在插入数据时一直显示子查询返回的值不止一个
CREATE TRIGGER [DBO].[TRIGGER_1] ON [DBO].[OUTR]
AFTER INSERT
AS
BEGIN
DECLARE @INSERTED_SNO CHAR(15)
SET @INSERTED_SNO=(SELECT SNO FROM INSERTED)
UPDATE SSTA SET SSTATE ='离开' WHERE SNO IN(SELECT SNO FROM SSTA WHERE SNO=@INSERTED_SNO)
IF (SELECT SNO FROM RR)=@INSERTED_SNO AND (SELECT SEATNO FROM SEAT)=(SELECT RN FROM RR WHERE SNO=@INSERTED_SNO)
UPDATE SEAT SET SEATSTATE='空闲' WHERE SEATNO IN( SELECT SEATNO FROM SEAT WHERE SEATNO=@INSERTED_SNO)
END
盲猜是做比较的等号两边的某个SQL语句查询得到的结果不止一个，导致没法做比较