button not working when i insert new data - mysql

Question

when I input data are not yet available. button does not work
but when I enter existing data in the database, the button work for find existing records in the database and msgbox.appear
this my coding. (i am using Microsoft Visual Basic 2008 express edition database mysql)
Imports MySql.Data.MySqlClient
Public Class Form2
Public conn As MySqlConnection
Private Sub Form2_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
Application.DoEvents()
Button1.Focus()
conn = New MySqlConnection
'conn.ConnectionString = "server=localhost;database=ilmu;userid=root;password= ''"
Try
conn.Open()
Catch ex As Exception
MessageBox.Show("Error1: " & ex.Message)
End Try
End Sub
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
conn = New MySqlConnection("server=localhost;database=ilmu;userid=root;password= ''")
Try
conn.Open()
Dim sqlquery As String = "SELECT * FROM visitor WHERE nama = '" & TextBox1.Text & "';"
Dim data As MySqlDataReader
Dim adapter As New MySqlDataAdapter
Dim command As New MySqlCommand
command.CommandText = sqlquery
command.Connection = conn
adapter.SelectCommand = command
data = command.ExecuteReader
While data.Read()
If data.HasRows() = True Then
If data(2).ToString = TextBox2.Text Then
command = New MySqlCommand
command.Connection = conn
tkhupd = Now.ToString("yyyy-MM-dd HH:mm:tt")
command.CommandText = "INSERT INTO visitor(noK,khupd)VALUES ('" & TextBox1.Text & "','" & tkhupd & "')"
command.ExecuteNonQuery()
MessageBox.Show(" Berjaya, Sila Masuk. ", "Tahniah", MessageBoxButtons.OK, MessageBoxIcon.Information)
Else
MsgBox("exist")
End If
Else
MsgBox("Failed Login.")
End If
End While
Catch ex As Exception
End Try
End Sub
End Class

Answer 1

I am not sure what you are trying to do when there is not matching record in the database, but you don't have any code that would be hit in the case of no matching entries.
If there are no matching records, your while condition isn't met and nothing in the loop happens.
Fixing it likely involves rearranging the order of your loop and your if condition.
Check to see if data.hasRows first.
Example:
If data.HasRows() = True Then
While Data.Read
//code here for found rows
End While
Else
//code for no matching entries
End If
And as has been mentioned in Joel's comment, you really should look at using parameterized queries.
example of your insert command altered:
command.CommandText = "INSERT INTO visitor(noK,khupd)VALUES (?noK,?khupd)"
command.Parameters.AddWithValue("?noK",TextBox1.Text)
command.Parameters.AddWithValue("?khupd", tkhupd)
command.ExecuteNonQuery()