Question

我有一个这样的查询，查看不同网址的负载，并按主机名对它们进行分组。它非常难看，但似乎足够快。

如何编写它以便丑陋的子串（抓取域的第一部分）以更整洁的方式编写？我正在从一系列社交媒体网站生成查询，因此可能会有更多网站。

SELECT substring(r.name, 8, locate("/",substring(r.name FROM 8))-1) AS referer_domain,
       count(USER) AS hits,
       r.id
FROM core c,
     referer r
WHERE c.site_url = 12
    AND r.name LIKE '%/%'
    AND c.referer = r.id
    AND (substring(r.name, 8, locate("/",substring(r.name FROM 8))-1) = "www.delicious.com"
    OR substring(r.name, 8, locate("/",substring(r.name FROM 8))-1) = "www.facebook.com"
    OR substring(r.name, 8, locate("/",substring(r.name FROM 8))-1) = "m.facebook.com"
    OR substring(r.name, 8, locate("/",substring(r.name FROM 8))-1) = "www.reddit.com"
    OR substring(r.name, 8, locate("/",substring(r.name FROM 8))-1) = "twitter.com"
    OR substring(r.name, 8, locate("/",substring(r.name FROM 8))-1) = "news.ycombinator.com"
GROUP BY substring(r.name, 8, locate("/",substring(r.name FROM 8))-1)
ORDER BY hits DESC

Answer 1

在您的情况下，您已经创建了一个输出列referer_domain，您可以参考GROUP BY。

为了在WHERE子句中使用它，尽管你需要一个视图。

CREATE VIEW ref_domain_view AS SELECT *,substring(name, 8, locate("/",substring(name FROM 8))-1) as referer_domain FROM referer;

SELECT r.referer_domain,
   count(USER) AS hits,
   r.id
FROM core c,
 ref_domain_view r
WHERE c.site_url = 12
AND r.name LIKE '%/%'
AND c.referer = r.id
AND referer_domain = "www.delicious.com"
OR referer_domain = "www.facebook.com"
OR referer_domain = "m.facebook.com"
OR referer_domain = "www.reddit.com"
OR referer_domain = "twitter.com"
OR referer_domain = "news.ycombinator.com"
GROUP BY referer_domain
ORDER BY hits DESC

Answer 2

您可以使用CREATE FUNCTION。

Answer 3

这样做的一种方法是编写一个用于字符串提取的user-defined function (UDF)。 UDF速度很快，但写起来却更加痛苦。另一种方法是编写一个stored function类型的存储过程，它更易于编写，更符合SQL语法。

Answer 4

虽然以上两个答案都有很好的观点，但我必须问你一些事情。

你真的需要所有的子串函数调用吗？

你有没有试过这样的事情：

SELECT substring(r.name, 8, locate("/",substring(r.name FROM 8))-1) AS referer_domain,
   count(USER) AS hits,
   r.id
FROM core c,
 referer r
WHERE c.site_url = 12
AND r.name LIKE '%/%'
AND c.referer = r.id
AND r.name    = "http://www.delicious.com"
OR r.name     = "http://www.facebook.com"
OR r.name     = "http://m.facebook.com"
OR r.name     = "http://www.reddit.com"
OR r.name     = "http://twitter.com"
OR r.name     = "http://news.ycombinator.com"
GROUP BY substring(r.name, 8, locate("/",substring(r.name FROM 8))-1)
ORDER BY hits DESC

上述查询的唯一问题是，如果您需要更多域来跟踪您需要更改查询。如果将域放入表中并加入到该表中，则可能完全摆脱子字符串，也不必更改查询。

如何以干燥的方式编写MYSQL查询

4 个答案: