请问，我的SQL语法错在哪里？

[applehoo]

Tj1 = "[表1].[编号] = [表2].[编号]"
Tj2 = "[表1].[值1]=''"
Tj3 = "[表1].[值2]=''"
Tj4 = "[表1].[值3]=''"
Tj5 = "([表2].[日期]-[表2].[日期])>=28"
Tj = Tj1 & " And " & Tj2 & " And " & Tj3 & " And " & Tj4 & " And " & Tj5
Sql = "SELECT * FROM [表1],[表2] Where " & Tj & " ORDER BY [表1].[编号]"

[OpenVMS]

Tj2 = "len([表1].[值1])=0"
Tj3 = "len([表1].[值2])=0"
Tj4 = "len([表1].[值3])=0"

[I_wanttoknow]

up
null用''判断不出来

[ssq1978]

Tj2 = "[表1].[值1] is null"
Tj3 = "[表1].[值2] is null"
Tj4 = "[表1].[值3] is null"

[applehoo]

谢谢各位，我的Tj5过不去，如何写才是正确的呢？

日期字段是字符型的。

[applehoo]

条件5是[表2].[日期1]-[表2].[日期2]

[zjcxc]

字符型的要用类型转换
Tj5 = "(cast([表2].[日期] as datetime)-cast([表2].[日期] as datetime))>=28"

[zjcxc]

条件2-4还可以改为:
Tj2 = "isnull([表1].[值1],'')=''"
Tj3 = "isnull([表1].[值2],'')=''"
Tj4 = "isnull([表1].[值3],'')=''"

[applehoo]

谢谢各位！