รบกวนดู Error ให้หน่อยนะคะ เกี่ยวกับ PRIMARY KEY คะ Violation of PRIMARY KEY constraint 'PK_Purchases'. Cannot insert duplicate key in object 'dbo.Purchases'.

Private Sub BTSave_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles BTSave.Click
        Dim sb As StringBuilder



        If TxtPurID.Text.Trim() = "" Then
            MessageBox.Show("กรุณากดปุ่มเพิ่มใบสั่งซื้อก่อน!!", "", MessageBoxButtons.OK, MessageBoxIcon.Information)
            Exit Sub
        End If

        If MessageBox.Show("คุณต้องการเพิ่มใบสั่งซื้อใช่หรือไม่", "", MessageBoxButtons.YesNo, MessageBoxIcon.Question) = Windows.Forms.DialogResult.No Then
            Exit Sub
        End If

        Dim sqlSave As String = ""

        sb = New StringBuilder()
        sb.Remove(0, sb.Length)
        sb.Append("INSERT INTO Purchases(PurID,SupplieID,Date,NetTotal)")
        sb.Append(" VALUES(@PurID,@SupID,@Date,@Tot)")
        sqlSave = sb.ToString()

        With cm
            .Parameters.Clear()
            .CommandText = sqlSave
            .Connection = cn
            cn.Open()
            .Parameters.AddWithValue("@PurID", TxtPurID.Text)
            .Parameters.AddWithValue("@SupID", CStr(ComboBox1.SelectedValue))
            .Parameters.Add("@Date", SqlDbType.DateTime).Value = TxtPurDate.Text
            .Parameters.Add("@Tot", SqlDbType.Float).Value = CSng(TxtTotal.Text)
            .ExecuteNonQuery()

        End With


        Dim i As Integer = 0

        For i = 0 To ListView1.Items.Count - 1
            sb.Remove(0, sb.Length)
            sb.Append("INSERT INTO PurchaseDetails (PurID,No,Amount,Price,Total)")
            sb.Append(" VALUES (@PurID,@NO,@Amount,@Price,@Tot)")
            sqlSave = sb.ToString()


            With cm

                .Parameters.Clear()
                .CommandText = sqlSave
                .Parameters.AddWithValue("@PurID", TxtPurID.Text)
                .Parameters.AddWithValue("@No", ListView1.Items(i).SubItems(1).Text)
                .Parameters.AddWithValue("@Amount", CInt(ListView1.Items(i).SubItems(4).Text))
                .Parameters.AddWithValue("@Price", CSng(ListView1.Items(i).SubItems(3).Text))
                .Parameters.Add("@Tot", SqlDbType.Float).Value = CSng(ListView1.Items(i).SubItems(5).Text)
                .ExecuteNonQuery()
            End With

            sb.Remove(0, sb.Length())
            sb.Append("UPDATE Products")
            sb.Append(" SET UnitInStock = @un")
            sb.Append(" WHERE (No=@ProID)")

            Dim sqlUP As String
            sqlUP = sb.ToString()

            With cm
                .Parameters.Clear()
                .CommandText = sqlUP
                .Parameters.AddWithValue("@un", CInt(ListView1.Items(i).SubItems(6).Text))
                .Parameters.AddWithValue("@ProID", ListView1.Items(i).SubItems(1).Text)
                .ExecuteNonQuery()

            End With

        Next

        MessageBox.Show("บันทึกข้อมูลเรียบร้อยแล้ว")

        cn.Close()
    End Sub
End Class