How can I make a recursive query?

Hello everybody,

I finally could populate a combobox in VB.NET with data grabbed from a remote MySQL DB. The problem is that that data, only fills the combobox but doesn't store the query results in an array or anything. What I need to do now, is to validate the selected user with the DB, while making the password MD5 hashed. This MD5 encrypt is easy, but I don't know why I can't make the second query to fetch the password for the selected user in the combobox (making a last name, first name comparation).

Here's my code:

Private Sub comUsername_TextChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles comUsername.TextChanged
        If comUsername.Text <> "" Then
            txtPassword.Enabled = True
            Dim user_full_name As String
 
            user_full_name = comUsername.Text
 
            SQL2 = "SELECT user_id FROM users WHERE 'user_last_name, user_name' = @user_full_name"
            myCommand.Connection = conn
            myCommand.CommandText = SQL2
 
            myAdapter.SelectCommand = myCommand
            myAdapter.Fill(myData)
 
            oReader = myCommand.ExecuteReader
 
            selected_user_id = oReader("user_id")
 
            MsgBox(selected_user_id)
 
            oReader.Close()
 
        Else
            txtPassword.Text = ""
            txtPassword.Enabled = False
        End If
    End Sub

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