一个SQL语句的问题，急死我了，请帮帮忙！！！ (30分)

[?]定义一个存储过程，代码如下：
CREATE PROCEDURE QueryJiaTai @starttime char(19),@houseid int AS
DECLARE @request char(19)
DECLARE @opensum int
DECLARE @destsum int
SET @opensum=(SELECT COUNT(insymbol) AS total FROM opentables WHERE starttime=@starttime)
SET @request=(SELECT request FROM opentables WHERE starttime=@starttime AND destine=1)
SET @destsum=(SELECT COUNT(insymbol) AS total FROM desttable WHERE request=@request)
IF @opensum>0 AND @destsum=0
SELECT id
FROM tables
WHERE houseid=@houseid
AND insymbol NOT IN (SELECT insymbol FROM opentables WHERE starttime=@starttime)
ELSE IF @destsum>0 AND @opensum=0
SELECT id
FROM tables
WHERE houseid=@houseid
AND insymbol NOT IN (SELECT insymbol FROM desttable WHERE request=@request)
ELSE IF @opensum>0 AND @destsum>0
SELECT id
FROM tables
WHERE houseid=@houseid
AND insymbol NOT IN (SELECT insymbol FROM opentables WHERE starttime=@starttime)
AND insymbol NOT IN (SELECT insymbol FROM desttable WHERE request=@request)
最后一种情况下，执行不正确，不知道如何实现最后这种情况？

怎么不正确？

在最后一种情况下，实际上有符合条件的记录，可是结果却返回空

是不是你的条件不对

是不是要注意一下运算符的优先级.