The system should not insert selected records from my datagridviewcheckboxcolumn if it's already existed in the database.

It's like when you're registering online. If you're username/email address already registered,it would inform you that youre username/email is already registered and the site would ask you to change your username/email to new ones.

The difference in my system is that i have 2 datagridviewcheckbox columns not just textboxes . Parent and Child in the datagridview. What i want to happen is that once the Code has been registered as Parent it cant be registered again as Child anymore.

I dont have a logic on that so far, i hope some could help me out here, but here's my code so far.

Code:
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Try

            connectionString = ";"
            sql_connection = New SqlConnection(connectionString)
            Dim cmdText As String = "INSERT INTO Conso_Holder (CONSO_PARENT_STOCKHOLD_CODE, CONSO_CHILD_STOCKHOLD_CODE, CONSO_STOCK_NAME) VALUES (@CONSO_PARENT_STOCKHOLD_CODE, @CONSO_CHILD_STOCKHOLD_CODE, @CONSO_STOCK_NAME)"
            Dim cmdTextDelChild As String = "DELETE Conso_Holder WHERE CONSO_CHILD_STOCKHOLD_CODE = @CONSO_CHILD_STOCKHOLD_CODE"
            Dim command As New SqlCommand(cmdText, sql_connection)
            Dim command2 As New SqlCommand(cmdTextDelChild, sql_connection)
            Dim parentCode As String = ""


            For i As Integer = 0 To DataGridView1.Rows.Count - 1
                If CBool(DataGridView1.Rows(i).Cells(0).Value) = True Then
                    parentCode = DataGridView1.Rows(i).Cells(2).Value.ToString

                    Exit For
                End If
            Next i

            For i As Integer = 0 To DataGridView1.Rows.Count - 1

                If CBool(DataGridView1.Rows(i).Cells(1).Value) = True Then

                    command2.Parameters.AddWithValue("@CONSO_CHILD_STOCKHOLD_CODE", DataGridView1.Rows(i).Cells(2).Value)
                    sql_connection.Open()
                    command2.ExecuteNonQuery()
                    sql_connection.Close()
                    command2.Parameters.Clear()
                End If
            Next i


            For i As Integer = 0 To DataGridView1.Rows.Count - 1

                sql_connection.Open()

                Dim slcString As String = " SELECT CONSO_PARENT_STOCKHOLD_CODE FROM Conso_Holder Where  CONSO_CHILD_STOCKHOLD_CODE = @CONSO_CHILD_STOCKHOLD_CODE "

                Dim command4 As New SqlCommand(slcString, sql_connection)

                'command4.Parameters.AddWithValue("@CONSO_PARENT_STOCKHOLD_CODE", parentCode)
                command4.Parameters.AddWithValue("@CONSO_CHILD_STOCKHOLD_CODE", DataGridView1.Rows(i).Cells(2).Value)

                datareadersql = command4.ExecuteReader

                'If CInt(datareadersql.HasRows) = 0 Then
                '    sql_connection.Close()


                '    MsgBox("Records Inserted")

                '    Exit For

                'ElseIf CInt(datareadersql.HasRows) <> 0 Then

                '    MsgBox("Records can't be inserted")

                '    Exit For


                'End If


                sql_connection.Open()
                Dim result As String = command4.ExecuteScalar.ToString
                sql_connection.Close()
                command4.Parameters.Clear()
            Next i






            For i As Integer = 0 To DataGridView1.Rows.Count - 1
                If CBool(DataGridView1.Rows(i).Cells(1).Value) = True Then
                    command.Parameters.AddWithValue("@CONSO_PARENT_STOCKHOLD_CODE", parentCode)
                    command.Parameters.AddWithValue("@CONSO_CHILD_STOCKHOLD_CODE", DataGridView1.Rows(i).Cells(2).Value)
                    command.Parameters.AddWithValue("@CONSO_STOCK_NAME", DataGridView1.Rows(i).Cells(3).Value)

                    sql_connection.Open()
                    command.ExecuteNonQuery()
                    sql_connection.Close()
                    command.Parameters.Clear()
                End If

            Next i





            Dim hasParentCode As Boolean = False
            For i As Integer = 0 To DataGridView1.Rows.Count - 1
                If CBool(DataGridView1.Rows(i).Cells(0).Value) = True Then
                    hasParentCode = True
                    Exit For
                End If
            Next
            If hasParentCode = False Then
                MsgBox("Select a Parent Code first.", vbInformation, "STO Masterfile System")
            End If


            Dim hasChildCode As Boolean = False
            For i As Integer = 0 To DataGridView1.Rows.Count - 1
                If CBool(DataGridView1.Rows(i).Cells(1).Value) = True Then
                    hasChildCode = True
                    Exit For
                End If
            Next
            If hasChildCode = False Then
                MsgBox("Select atleast one Child Code first.", vbInformation, "STO Masterfile System")
            End If

        Catch ex As Exception
            MsgBox(ex.Message)

        End Try
        itemlist.Clear()


    End Sub
I tried this but still not wrking.

Code:
  For i As Integer = 0 To DataGridView1.Rows.Count - 1

                sql_connection.Open()

                Dim slcString As String = " SELECT CONSO_PARENT_STOCKHOLD_CODE FROM Conso_Holder Where  CONSO_CHILD_STOCKHOLD_CODE = @CONSO_CHILD_STOCKHOLD_CODE "

                Dim command4 As New SqlCommand(slcString, sql_connection)

                'command4.Parameters.AddWithValue("@CONSO_PARENT_STOCKHOLD_CODE", parentCode)
                command4.Parameters.AddWithValue("@CONSO_CHILD_STOCKHOLD_CODE", DataGridView1.Rows(i).Cells(2).Value)

                datareadersql = command4.ExecuteReader

                'If CInt(datareadersql.HasRows) = 0 Then
                '    sql_connection.Close()


                '    MsgBox("Records Inserted")

                '    Exit For

                'ElseIf CInt(datareadersql.HasRows) <> 0 Then

                '    MsgBox("Records can't be inserted")

                '    Exit For


                'End If


                sql_connection.Open()
                Dim result As String = command4.ExecuteScalar.ToString
                sql_connection.Close()
                command4.Parameters.Clear()
            Next i
Please review my code

Thanks