php – MySQL：如何通过( – )破折号排序

例如,我在下面有这些数据,

page_id   url
1         - a
2         - b
3         --- c
4         --- d
5         - e
6         - f
7         -- g
8         -- h

我追求的结果,

page_id   url
1         - a
2         - b
5         - e
6         - f
7         -- g
8         -- h
3         --- c
4         --- d

如果我这样做,

ORDER by x.url ASC

我还是这个,

page_id   url
1         - a
2         - b
3         --- c
4         --- d
5         - e
6         - f
7         -- g
8         -- h

有任何想法吗？

编辑：

我的实际SQL,

SELECT 
    *,IF(grandparentURL REGEXP '^[a-z0-9-]+$',CONCAT('--- ',url),IF(parentURL REGEXP '^[a-z0-9-]+$',CONCAT('-- ',CONCAT('- ',url))) AS url
FROM
(
    SELECT 
        p.page_id,p.url,p2.url AS parentURL,p3.url AS grandparentURL

    FROM page AS p

    LEFT JOIN page AS p2 
    ON p.parent_id = p2.page_id AND p.page_id != p2.page_id

    LEFT JOIN page AS p3 
    ON p2.parent_id = p3.page_id AND p2.page_id != p3.page_id

    WHERE IF('5' REGEXP '^[0-9]+$',p.page_id != '5',p.page_id IS NOT NULL)
    AND p.url != 'cms' 
) x

ORDER by x.url ASC