MySQL计算多个外键

Question

所以我有一个查询，我从“站点”表中选择，并使用外键计算“页面”的数量

SELECT s_id, s_name, s_main_url, COUNT(p_id) AS numpages
FROM sites
INNER JOIN pages ON sites.s_id = pages.site_id
GROUP BY pages.site_id
ORDER BY s_id ASC

我想添加另一个外键来计数，可能不止一个，所以我尝试了以下

SELECT s_id, s_name, s_main_url, COUNT(p_id) AS numpages, COUNT(l_id) AS numlinks
FROM sites
INNER JOIN pages ON sites.s_id = pages.site_id
INNER JOIN links ON sites.s_id = links.site_id
GROUP BY pages.site_id, links.site_id
ORDER BY s_id ASC

numpages 和 numlinks 的计数是相同的，它们似乎将所有表的结果相乘，给我一些不正确的巨大数字

有什么想法吗？

Answer 1

您应该考虑使用子选择而不是 JOIN 和 GROUP BY。

SELECT s_id, s_name, s_main_url, numpages, numlinks
FROM sites, 
(SELECT COUNT(p_id) as numpages FROM pages WHERE pages.site_id = sites.s_id) as cnt_pages,
(SELECT COUNT(l_id) as numlink FROM links WHERE links.site_id = sites.s_id) as cnt_links
ORDER BY s_id ASC