vb查询数据库问题

    txtSQL2 = "select * from s_student where 班级 = '" & Combo2.Text & "'"
        cmd.CommandText = txtSQL2
        Set mrc = cmd.Execute
        While (mrc.EOF = False)
        Combo3.AddItem mrc.Fields(0)
        mrc.MoveNext
        Wend
        mrc.Close
求救，为什么查询不到我想要的值？