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()