I have a question about this line of code, see below

    //Initialize variables.
    $db = JFactory::getDbo();
    $query = $db->getQuery(true);
    
    //Create the base select statement.
    $query->select('a.id as id, a.greeting as greeting, a.published as published')->from($db->quoteName('#__diolegend','a'));
    
    //Join over the categories.
    $query->select($db->quoteName('c.title' ,'category_title'))->join('LEFT',$db->quoteName('#__categories','c')
        . ' ON c.id =a.catid');

    $query->select($db->quoteName('c.title' ,'category_title'))->join('LEFT',$db->quoteName('#__categories','c')
        . ' ON c.id =a.catid');

How can it be possible to still retrieve a.catid, we haven't select from anywhere...

Thank you everybody