如何停止調用函數繼續向下執行

我寫了個調用函數:
Public Sub ChkOnly(ByVal sqlstr As String, ByVal chkname As String)
        Dim constr As String = My.Settings.constr
        Dim con As New SqlConnection(constr)
        Dim ds As New DataSet
        Try
            con.Open()
            Dim da As New SqlDataAdapter(sqlstr, con)
            da.Fill(ds)
            con.Close()
            con.Dispose()
            If ds.Tables(0).Rows.Count <> 0 Then
                MsgBox("已經存在此" & chkname, MsgBoxStyle.Critical, "提示")
                Exit Sub
            End If
        Catch ex As Exception
            MsgBox(ex.Message, MsgBoxStyle.Critical, "提示")
            Exit Sub
        End Try
    End Sub

點擊新增按鈕(btn_add)觸發的執行函數,新增前,我檢查數據庫表裡是否已經存在同樣的數據.代易做图如下:

Dim sqlstr_chk As String = "select ply from MTPm where MType='" & Trim(Me.Cbx_MMtype.Text) & "'"
        ChkOnly(sqlstr_chk, "機種")
Dim sqlstr As String = "insert into MTPm values('" & Trim(Me.Cbx_MPly.Text) & "','" & Trim(Me.Cbx_MMtype.Text) & "'," & Val(Trim(Me.Tbx_FstckAlarm1.Text)) & _
        "," & Val(Trim(Me.Tbx_FstckAlarm2.Text)) & "," & Val(Trim(Me.Tbx_OQCAlarm1.Text)) & "," & Val(Trim(Me.Tbx_OQCAlarm2.Text)) & "," & Val(Trim(Tbx_pdct_x1.Text)) & "," & Val(Trim(Tbx_pdct_x2.Text)) & ")"
        sqlexcute(sqlstr, "新增機種")
''''''sqlexcute()是執行SQL語句的調用函數.

在執行ChkOnly()要新增的數據已經存在時候,停止執行調用函數下面的代易做图,即  :
dim sqlstr,sqlexcute()....

請問這樣的功能怎麼實現啊?我分沒了,請好心的高手幫忙指點一下.

--------------------编程问答-------------------- 可以在前面加個判斷數據是否存在，再新增。。。
if 條件 then
存在則：
else
不存在
end if --------------------编程问答-------------------- 我觉得可以把ChkOnly这个函数改写一下，改成直接返回一个DataTable
然后
Dim   sqlstr_chk   As   String   =   "select   ply   from   MTPm   where   MType='"   &   Trim(Me.Cbx_MMtype.Text)   &   "'"
     dim dt as DataTable=ChkOnly(sqlstr_chk,   "機種")
if dt.Tables(0).Rows.count=0 Then
Dim   sqlstr   As   String   =   "insert   into   MTPm   values('"   &   Trim(Me.Cbx_MPly.Text)   &   "','"   &   Trim(Me.Cbx_MMtype.Text)   &   "',"   &   Val(Trim(Me.Tbx_FstckAlarm1.Text))   &   _
                ","   &   Val(Trim(Me.Tbx_FstckAlarm2.Text))   &   ","   &   Val(Trim(Me.Tbx_OQCAlarm1.Text))   &   ","   &   Val(Trim(Me.Tbx_OQCAlarm2.Text))   &   ","   &   Val(Trim(Tbx_pdct_x1.Text))   &   ","   &   Val(Trim(Tbx_pdct_x2.Text))   &   ")"
                sqlexcute(sqlstr,   "新增機種")
else
   messagebox.show("机种已存在！")
Cbx_MMtype.focus()
exit sub

补充：.NET技术 ,  VB.NET