most userful joomla function to debug database query

// Get a db connection.
$db = JFactory::getDbo();
 
// Create a new query object.
$query = $db->getQuery(true);
 
// Select all articles for users who have a username which starts with 'a'.
// Order it by the created date.
// Note by putting 'a' as a second parameter will generate `#__content` AS `a`
$query
    ->select($db->quoteName(array('a.*', 'b.username', 'b.name')))
    ->from($db->quoteName('#__content', 'a'))
    ->join('INNER', $db->quoteName('#__users', 'b') . ' ON (' . $db->quoteName('a.created_by') . ' = ' . $db->quoteName('b.id') . ')')
    ->where($db->quoteName('b.username') . ' LIKE \'a%\'')
    ->order($db->quoteName('a.created') . ' DESC');

// echo sql query so you can see it and debug it ;)
echo $db->replacePrefix( (string) $query );
 
// Reset the query using our newly populated query object.
$db->setQuery($query);

// Get array with information of the query
$rows = $db->loadAssocList();