存储过程sql语句拼合有错，但不知道怎么改，希望帮忙改一下。
存储过程代码：
USE [HLJSXKJSYYJSGLPT]
GO
/****** Object: StoredProcedure [dbo].[GetSSYJSFZYLYXSSTJ] Script Date: 03/24/2012 10:30:26 ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
-- =============================================
-- Author: <Author,,Name>
-- Create date: <Create Date,,>
-- Description: <Description,,>
-- =============================================
ALTER PROCEDURE [dbo].[GetSSYJSFZYLYXSSTJ]
@xxkyjg nvarchar(20),@tjny char(6)
AS
begin
declare @sql nvarchar(200);
set @sql = 'insert into T_YJSXX_'+@xxkyjg+'_SS_TJ
select 
COUNT(case when jbxxb.HXWRQ IS NOT NULL then 1 else 0 end) as 授予学位数,
COUNT(case when jbxxb.RXNY >= '+@tjny+' then 1 else 0 end) as 招生数合计,
COUNT(case when substring(RXNY,1,4)=substring('+@tjny+',1,4) then 1 else 0 end) as 招生应届生数,
COUNT(case when CAST(substring(RXNY,1,4) AS INT)+1 = substring('+@tjny+',1,4) then 1 else 0 end) as 在校一年级生数,
COUNT(case when CAST(substring(RXNY,1,4) AS INT)+2 = substring('+@tjny+',1,4) then 1 else 0 end) as 在校二年级生数,
COUNT(case when CAST(substring(RXNY,1,4) AS INT)+3 = substring('+@tjny+',1,4) then 1 else 0 end) as 在校三年级生数,
COUNT(case when CAST(substring(RXNY,1,4) AS INT) > substring('+@tjny+',1,4) then 1 else 0 end) as 在校生合计,
COUNT(case when CAST(substring(RXNY,1,4) AS INT)+3 = substring('+@tjny+',1,4) then 1 else 0 end) as 预计毕业生数,
xwlx.XWLX as 学位类型, pyfs.PYFS as 评优方式, xb.XB as 性别, zy.ZY as 专业 
from T_YJSXX_'+@xxkyjg+'_SS jbxxb  
inner join T_XWLX xwlx on jbxxb.XWLXM=xwlx.XWLXM
inner join T_PYFS pyfs on jbxxb.PYFSM=pyfs.PYFSID
inner join T_XB xb on jbxxb.XBM=xb.XBM
inner join T_ZY zy on jbxxb.ZYDM=zy.ZYM
group by xwlx.XWLX, pyfs.PYFS, xb.XB, zy.ZY';
EXEC(@sql);
END

网站运行时出错提示：在应使用条件的上下文(在 'substr' 附近)中指定了非布尔类型的表达式。
按我自己的各种测试之后的推断，错就出在语句拼合substring传参这块。

------解决方案--------------------

SQL code

ALTER PROCEDURE [dbo].[GetSSYJSFZYLYXSSTJ] @xxkyjg nvarchar(20),@tjny char(6)
AS
begin
  declare @sql nvarchar(200);
  set @sql = 'insert into T_YJSXX_' + @xxkyjg + '_SS_TJ 
select  
COUNT(case when jbxxb.HXWRQ IS NOT NULL then 1 else 0 end) as 授予学位数,
COUNT(case when jbxxb.RXNY >= ''' + @tjny + ''' then 1 else 0 end) as 招生数合计,
COUNT(case when substring(RXNY,1,4)=substring('+@tjny+',1,4) then 1 else 0 end) as 招生应届生数,
COUNT(case when CAST(substring(RXNY,1,4) AS INT)+1 = substring('+@tjny+',1,4) then 1 else 0 end) as 在校一年级生数,
COUNT(case when CAST(substring(RXNY,1,4) AS INT)+2 = substring('+@tjny+',1,4) then 1 else 0 end) as 在校二年级生数,
COUNT(case when CAST(substring(RXNY,1,4) AS INT)+3 = substring('+@tjny+',1,4) then 1 else 0 end) as 在校三年级生数,
COUNT(case when CAST(substring(RXNY,1,4) AS INT) > substring('+@tjny+',1,4) then 1 else 0 end) as 在校生合计,
COUNT(case when CAST(substring(RXNY,1,4) AS INT)+3 = substring('+@tjny+',1,4) then 1 else 0 end) as 预计毕业生数,
xwlx.XWLX as 学位类型, pyfs.PYFS as 评优方式, xb.XB as 性别, zy.ZY as 专业  
from T_YJSXX_'+@xxkyjg+'_SS jbxxb   
inner join T_XWLX xwlx on jbxxb.XWLXM=xwlx.XWLXM
inner join T_PYFS pyfs on jbxxb.PYFSM=pyfs.PYFSID
inner join T_XB xb on jbxxb.XBM=xb.XBM
inner join T_ZY zy on jbxxb.ZYDM=zy.ZYM
group by xwlx.XWLX, pyfs.PYFS, xb.XB, zy.ZY'

EXEC(@sql);

END