[Visual Basic] .NET จะเชียนกรองคำก่อนลงฐานข้อมูลยังไงดีครับ

Imports MySql.Data.MySqlClient
Imports System.Data

Public Class txtage

    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

    End Sub

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Dim Conn As MySqlConnection
        Conn = New MySqlConnection()

        Conn.ConnectionString = "Server=203.101.30.57; Database=xxxxx; Uid=xxxx; Pwd=xxxx; Character Set=utf8;"
        Try
            Conn.Open()
        Catch myerror As MySqlException
            MsgBox("ติดต่อฐานข้อมูลไม่ได้")
        End Try
        Dim myAdapter As New MySqlDataAdapter

        Dim sqlquery = "SELECT * FROM data WHERE code = '" + txtcode.Text + "' "
        Dim Mycommand As New MySqlCommand()
        Mycommand.Connection = Conn
        Mycommand.CommandText = sqlquery

        myAdapter.SelectCommand = Mycommand
        Dim mydata As MySqlDataReader
        mydata = Mycommand.ExecuteReader()
        If mydata.HasRows = 0 Then

            Conn.Close()
            Conn.Open()



            sqlquery = " INSERT INTO data (day, month, year,nickname,age,sex,class,subj_head,subj_punha,subj_pon,type,code) VALUES ('" + txtdate.Text + "','" + txtmonth.Text + "','" + txtyear.Text + "','" + txtnickname.Text + "','" + txtage2.Text + "','" + txtsex.Text + "','" + txtclass.Text + "','" + txtsubj_head.Text + "','" + txtpunha.Text + "','" + txtpon.Text + "','ยังไม่ได้แก้ไข','" + txtcode.Text + "')"
            Mycommand.Connection = Conn
            Mycommand.CommandText = sqlquery

            mydata = Mycommand.ExecuteReader()
            MsgBox("บันทึกข้อมูลสู่ระบบแล้ว")

            Conn.Close()
            Me.Hide()
        Else
            index.Show()


        End If

    End Sub

    Private Sub txtclass_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles txtclass.SelectedIndexChanged

    End Sub
End Class