vb+Access 改成VB+SQL 所遇到的问题

各位大虾：
下面程序本来是VB+Access的，后来被我改成VB+SQL的。运行时在“Dat_Main.rsDat_class.State = 1”处报错，请问怎么改啊？


Private Sub Command1_Click()
Dim SQLoriginal As String
Dim SQLadd As String
Dim SQLorder As String
Dim strSql As String

SQLoriginal = "SELECT 年级,院系,专业,人数,辅导员,班长,备注 FROM 班级表 "
SQLadd = "WHERE 年级=年级 AND 专业=专业 "
SQLorder = ""

If Check1.Value = 1 And IsNumeric(Text1) Then
SQLadd = SQLadd + "and 年级='" + Text1 + "'"
End If

If Check2.Value = 1 And Not IsNull(Text2) Then
SQLadd = SQLadd + "and 专业='" + Text2 + "'"
End If

If Check3.Value = 1 And IsNumeric(Text3) Then
SQLadd = SQLadd + "and 人数='" + Text3 + "'"
End If

If Check4.Value = 1 And Not IsNull(Text4) Then
SQLadd = SQLadd + "and 辅导员='" + Text4 + "'"
End If

strSql = SQLoriginal + SQLadd + SQLorde

If Dat_Main.rsDat_class.State = 1 Then
Dat_Main.rsDat_class.Close
End If

Dat_Main.rsDat_class.Open strSql
Dat_Class.Show vbModal
Text1.Text = ""
Text2.Text = ""
Text3.Text = ""
Text4.Text = ""

End Sub

Private Sub Command2_Click()
Unload Me
End Sub

Private Sub Form_Load()
Text1.Text = ""
Text2.Text = ""
Text3.Text = ""
Text4.Text = ""
End Sub