主题：表达式过于复杂

Dim s1 As Integer = val(Left("2017年秋季",4))
Dim SQL As String = "IIF(b.学期 Like '%秋%',IIF(('"& s1 &"' - val(Left(b.学期,4))) *100 + val(班级) < 1000,('"& s1 &"'- val(Left(b.学期,4))) *100 + val(班级)),IIF(b.学期 Like '%春%',IIF(('"& s1 &"' - val(Left(b.学期,4))) *100 + val(班级) < 1000,('"& s1 &"' - val(Left(b.学期,4))) *100 + val(班级))))"
Dim SQL1 As String = "IIF(Left(" & SQL & ",1) = 1,'一年级',IIF(Left(" & SQL & ",1) = 2,'二年级',IIF(Left(" & SQL & ",1) = 3,'三年级',IIF(Left(" & SQL & ",1) = 4,'四年级',IIF(Left(" & SQL & ",1) = 5,'五年级',IIF(Left(" & SQL & ",1) = 6,'六年级',IIF(Left(" & SQL & ",1) = 7,'七年级',IIF(Left(" & SQL & ",1) = 8,'八年级',IIF(Left(" & SQL & ",1)  = 9,'九年级')))))))))"
Dim SQL2 As String = "Select  b.学期,b.学生编号,学生姓名,"& SQL1 &" As 年级 Fr om (({学生基本信息} a Inner JOIN {缴退费信息} b ON a.学生编号 = b.学生编号) Inner JOIN {违规信息} c ON b.学生编号 = c.学生编号) Inner JOIN (Select 学生编号,max(缴费日期) As 缴费日期 Fr om {缴退费信息} WHERE 缴费项目 = '学费' And 缴费状态 = '已缴' GROUP BY 学生编号) n on b.学生编号 = n.学生编号 And b.缴费日期 = n.缴费日期 WHERE 缴费项目 = '学费' And 缴费状态 = '已缴' And c.审批状态 = '拒绝报名'"

错误信息：表达式过于复杂 在查询表达式 'IIF(Left(IIF(b.学期 Like '%秋%',IIF(('2017' - val(Left(b.学期,4))) *100 + val(班级) < 1000,('2017'- val(Left(b.学期,4))) *100 + val(班级)),IIF(b.学期 Like '%春%',IIF(('2017' - val(Left(b.学期,4))) *100 + val(班级) < 1000,('2017' - val(Left(b.学期,4))) *100 + val(班级)))),1) = ' 中。

请老师帮我看一下问题在哪？删除任意类似红色字段就可以，请老师执教，谢谢！