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VB.NET SQL statement doesn’t return any rows form Access database

I have the following code for a login winform. When I make the connection to the database and make a select statement I get no rows back. I’m getting the message “No data exists for the row/column.”

But there are rows and columns in the database.

Can someone tell me what I do wrong?

Private Sub OK_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles OK.Click
    Dim connectionString As String = System.Configuration.ConfigurationManager.ConnectionStrings("MySqlConnectionString").ConnectionString
    Using con As New OleDbConnection(connectionString)
        Dim intResult As Integer = 0
        ' MsgBox(connectionString)
        Try
            con.Open()

            Using cmd As New OleDbCommand("SELECT Gebruikersnaam FROM Gebruikers WHERE Gebruikers.Gebruikersnaam = @Username", con)
                cmd.Parameters.AddWithValue("@Username", UsernameTextBox.Text)
                cmd.Parameters.AddWithValue("@Password", PasswordTextBox.Text)
                Using dr As OleDbDataReader = cmd.ExecuteReader()

                    'intResult = CInt(cmd.ExecuteScalar)

                    'If intResult > 0 Then
                    MsgBox(dr.Item("Gebruikersnaam").ToString)
                    'End If

                    With dr
                        While .Read()
                            MsgBox(.HasRows)
                            'MsgBox(.Item("Gebruikersnaam"))
                            'TextBox1.Text = .Item("Gebruikersnaam") & vbCrLf
                        End While
                    End With
                End Using
            End Using

        Catch ex As Exception
            MsgBox(ex.Message)

            con.Close()
        End Try

        Me.Close()
    End Using
End Sub

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Answer

The problem was checking dr.Item() before ever calling dr.Read(). Aside from the that, make sure the username in UsernameTextBox actually exists in the database, fix those nasty plain-text passwords, and you’ll be fine.

Private Sub OK_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles OK.Click
    Dim connectionString As String = System.Configuration.ConfigurationManager.ConnectionStrings("MySqlConnectionString").ConnectionString
    Try
        Dim result As New StringBuilder()
        Using con As New OleDbConnection(connectionString)
        Using cmd As New OleDbCommand("SELECT Gebruikersnaam FROM Gebruikers WHERE Gebruikersnaam = @Username", con)

            cmd.Parameters.AddWithValue("@Username", UsernameTextBox.Text)
            cmd.Parameters.AddWithValue("@Password", PasswordTextBox.Text)
            con.Open()

             Using dr As OleDbDataReader = cmd.ExecuteReader()
                  While dr.Read() 
                      'MsgBox(dr("Gebruikersnaam"))
                      result.AppendLine(dr("Gebruikersnaam"))
                  End While
              End Using
        End Using
        End Using
        TextBox1.Text = result.ToString()
    Catch ex As Exception
        MsgBox(ex.Message)
    End Try
End Sub

One final concern. I’m not sure which OLE provider you’re using, but last time I checked most providers where it makes sense to use OLE want you to use ? placeholders instead of named parameters. So the SQL command would look like this:

SELECT Gebruikersnaam FROM Gebruikers WHERE Gebruikersnaam = ?

But if you’re really using MySql, as the connection string name suggests, you really do so much better getting the real MySql ADO.Net library instead of OleDB: minor performance gain, better error messaging, etc.

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