在 SQL 中编写子查询

Question

我正在学习 PostgreSQL，并且我有一个包含以下列的数据库日志：路径文本、ip inet、方法文本、状态文本、时间时间戳记、id int

使用此数据库，我的目标是找到错误百分比（状态！= '200 OK' / 状态）超过 2.5% 的任何日子。我有如下查询，它以小数形式得到错误百分比，但我不知道如何将它们乘以 10 以使它们成为“百分比”，也不知道如何检查它们是否超过 2.5。

我已经在多个地方同时尝试了 HAVING 和 WHERE，但是无论我在哪里输入 HAVING 或 WHERE，我都会在 group by 处遇到编程错误或语法错误。将其更改为百分比并检查其是否超过 2.5 的正确方法是什么？提前致谢

模拟数据：

CREATE TABLE log (
    path text,
    ip inet,
    method text,
    status text,
    "time" timestamp with time zone DEFAULT now(),
    id integer NOT NULL
);

INSERT INTO log VALUES ('/article/bears-love-berries', '198.51.100.76' , 'GET', '200 OK', '2016-07-1 12:54:22+00', 3355597);
INSERT INTO log VALUES ('/article/candidate-is-jerk', '198.51.100.76' , 'GET', '200 OK', '2016-07-1 19:54:22+00', 3355598);
INSERT INTO log VALUES ('/article/bears-love-berries', '198.51.100.76' , 'GET', '404 NOT FOUND', '2016-07-1 22:54:22+00', 3355599);
INSERT INTO log VALUES ('/article/goats-eat-googles', '203.0.113.42' , 'GET', '200 OK', '2016-07-11 12:54:22+00', 3355600);
INSERT INTO log VALUES ('/article/candidate-is-jerk', '203.0.113.42' , 'GET', '200 OK', '2016-07-11 17:54:22+00', 3355601);
INSERT INTO log VALUES ('/article/bears-love-berries', '203.0.113.42' , 'GET', '200 OK', '2016-07-11 19:54:22+00', 3355602);
INSERT INTO log VALUES ('/article/goats-eat-googles', '203.0.113.42' , 'GET', '404 NOT FOUND', '2016-07-15 13:54:22+00', 3355603);
INSERT INTO log VALUES ('/article/bears-love-berries', '198.51.100.34' , 'GET', '200 OK', '2016-07-15 20:54:22+00', 3355604);
INSERT INTO log VALUES ('/article/candidate-is-jerk', '198.51.100.34' , 'GET', '200 OK', '2016-07-15 23:54:22+00', 3355605);
INSERT INTO log VALUES ('/article/candidate-is-jerk', '203.0.113.12' , 'GET', '200 OK', '2016-07-21 19:54:22+00', 3355606);
INSERT INTO log VALUES ('/article/bears-love-berries', '203.0.113.12' , 'GET', '200 OK', '2016-07-21 12:54:22+00', 3355607);
INSERT INTO log VALUES ('/article/goats-eat-googles', '198.51.100.76' , 'GET', '200 OK', '2016-07-21 01:54:22+00', 3355608);
INSERT INTO log VALUES ('/article/goats-eat-googles', '198.51.100.76' , 'GET', '404 NOT FOUND', '2016-07-29 07:54:22+00', 3355609);
INSERT INTO log VALUES ('/article/candidate-is-jerk', '198.51.100.76' , 'GET', '404 NOT FOUND', '2016-07-29 20:54:22+00', 3355610);
INSERT INTO log VALUES ('/article/goats-eat-googles', '198.51.100.34' , 'GET', '200 OK', '2016-07-29 19:54:22+00', 3355611);

查询：

SELECT DATE(time) AS day,
(
  (SELECT CAST(COUNT(status) AS FLOAT)
  FROM log WHERE status != '200 OK') /
  (SELECT CAST(COUNT(status) AS FLOAT))
) AS views
FROM log GROUP BY day
ORDER BY views

Answer 1

在 sqlfiddle 中分享了一个测试用例后，我们可以着手编写一个可以运行的代码。

小提琴在这里：http://sqlfiddle.com/#!15/b3ed9/39

您可以只检查已经乘以 0.025 的结果，而不是将结果乘以 100，不是吗？我的意思是，如果您的值介于 0-1 之间，则相当于 2.5% 的值将仅为 0.025。

因此该命令应该这样做：

select views.day, views.cnt from
 (select datelog.day,
  (
   cast(count(case when datelog.status != '200 OK' then 1 else null end) as float)
   /
   cast(count(*) as float)
  ) as cnt
  from (select DATE(time) as day, status from log) as datelog
  group by datelog.day
 ) as views
 where views.cnt > 0.025

最后的修改深深植根于这里的回复：SQL use column from subselect in where clause