Select using -1 in tinyint field on MYSQL

Question

I have written the following code to filter the people who wants a newsletter via post or e-mail:

Sub loadoverviewnewsletter()
        Dim sql As String
        Dim sql1 As String
    If newslettermail = True Then
        sql = "SELECT * FROM Donateurs WHERE 'Newsletter per e-mail' =-1"
        sql1 = "SELECT * FROM Donateurs WHERE 'Newsletter per e-mail' =-1"
    ElseIf newsletterpost = True Then
        sql = "SELECT * FROM Donateurs WHERE 'Newsletter per post' =-1"
        sql1 = "SELECT * FROM Donateurs WHERE 'Newsletter per post' =-1"
    ElseIf newsletternew = True Then
        sql = "SELECT * FROM Donateurs WHERE 'Newsletter per post' =0 AND 'Nieuwsbrief per e-mail' =0"
        sql1 = "SELECT * FROM Donateurs WHERE 'Newsletter per post' =0 AND 'Nieuwsbrief per e-mail' =0"
    Else
        sql = "SELECT * FROM Donateurs"
        sql1 = "SELECT * FROM Donateurs"
    End If

    Dim adapter As New MySqlClient.MySqlDataAdapter(sql, modConnectorHandler.ServerString)
    Dim dt As New DataTable("newsletteroverview")
    adapter.Fill(dt)
    ShowDonateurs.datagrid.DataSource = dt

    ShowDonateurs.ShowDialog()
    Dim adapter1 As New MySqlClient.MySqlDataAdapter(sql1, modConnectorHandler.ServerString)
    Dim cmd1 As New MySqlClient.MySqlCommand(sql1, modConnectorHandler.mysqlconnection)
    modConnectorHandler.mysqlconnection.Open()
    Dim myreader As MySqlClient.MySqlDataReader = cmd1.ExecuteReader
    myreader.Read()
    modConnectorHandler.mysqlconnection.Close()
    OverviewNewsLetter.Close()

Unfortunately, it returns an empty datagrid, while when I select the newsletternew option, it shows the complete table. The fields "Newsletter per e-mail" and "Newsletter per post" are tinyint fields which can have the values -1 (means checked in application) and 0 (meand unchecked).

I really don't understand why it doesn't work.. I hope anyone can help.

Answer 1

You need to use the backticks instead of the single quotes for your column names. Consider this WHERE condition:

WHERE 'Newsletter per e-mail' =-1

It's comparing the string constant Newsletter per e-mail to -1. The result of the comparison is always false. Try this instead:

WHERE `Newsletter per e-mail` = -1

Now it's referring to a column name and not a string constant.

Finally, avoid column names that need backticks whenever possible (which is almost all the time). As you can see, they tend to lead to trouble.