Missing RECORD WANT to Add in Table

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VB

Hi. All...
I GET RECORD FORM STUDENTDATA and SAVE to MARKENTRY Table.

For Example: STUDENTDATA

RegNo	Name	Class	Section
A100      	AAA	I         	A         
A200      	BBB	I         	A         
A300      	CCC	I         	A         
			
			
			
MARK ENTRY ( HEre A200 Record is Missing but i want to ADD RECORD A200)i don't want to change Other REcord			
RegNo	Name	Class	Section
A100      	AAA	I         	A         
			
A300      	CCC	I         	A         

Here I Used Code For FIRST TIME NO RECORED MEANS Add New RECORED that work fine..

Next Time i want to Check MARKENTRY Talbe IF there some Recored Missing That Record Only I WANT TO ADD..

Dim strSQL8 As String = "SELECT * FROM MarkENTRY WHERE Class='" & cboClass.Text & "' and ExamDet='" & cboExType.Text & "'"
    Dim DaAp8 As New SqlDataAdapter(strSQL8, con)
    Dim Dset8 As New DataSet
        DaAp8.Fill(Dset8)



    Dim strSQL7 As String = "SELECT SD.Regno,SD.Sname,ED.ExamDet FROM StudentData as SD " & _
        " INNER JOIN Exam_List as ED ON SD.class='" & cboClass.Text & "' and ED.class='" & cboClass.Text & "'" ' and ED.ExamDet='" & cboExType.Text & "'"
    Dim DaAp7 As New SqlDataAdapter(strSQL7, con)
    Dim Dset7 As New DataSet
    DaAp7.Fill(Dset7)

        For i As Integer = 0 To Dset7.Tables(0).Rows.Count - 1
            vRegno = (Dset7.Tables(0).Rows(i).Item("Regno"))
            vSname = (Dset7.Tables(0).Rows(i).Item("Sname"))
            VEx_Type = (Dset7.Tables(0).Rows(i).Item("ExamDet"))
            con.Open()
            cmd.ExecuteNonQuery()
            con.Close()
        Next i
        MsgBox("Recored  Successfully Added")

Please tell me..