Method _getListCount

/**
 * Returns a record count for the query.
 *
 * Note: Current implementation of this method assumes that getListQuery() returns a set of unique rows,
 * thus it uses SELECT COUNT(*) to count the rows. In cases that getListQuery() uses DISTINCT
 * then either this method must be overridden by a custom implementation at the derived Model Class
 * or a GROUP BY clause should be used to make the set unique.
 *
 * @param   DatabaseQuery|string  $query  The query.
 *
 * @return  integer  Number of rows for query.
 *
 * @since   3.0
 */
protected function _getListCount($query)
{
    // Use fast COUNT(*) on DatabaseQuery objects if there is no GROUP BY or HAVING clause:
    if ($query instanceof DatabaseQuery && $query->type === 'select' && $query->group === null && $query->merge === null && $query->querySet === null && $query->having === null) {
        $query = clone $query;
        $query->clear('select')->clear('order')->clear('limit')->clear('offset')->select('COUNT(*)');
        $this->getDbo()->setQuery($query);
        return (int) $this->getDbo()->loadResult();
    }
    // Otherwise fall back to inefficient way of counting all results.
    // Remove the limit, offset and order parts if it's a DatabaseQuery object
    if ($query instanceof DatabaseQuery) {
        $query = clone $query;
        $query->clear('limit')->clear('offset')->clear('order');
    }
    $this->getDbo()->setQuery($query);
    $this->getDbo()->execute();
    return (int) $this->getDbo()->getNumRows();
}