Question

我有一个创建的视图，名称为author_article_log，如下所示：

              title              |          name          | status |    date
Candidate is jerk, alleges rival | Rudolf von Treppenwitz | 200 OK | 2016-07-01

我的工作是获取一天中请求错误的百分比，我的查询是：

select i.date, 
       ((count (case when i.status = '404 NOT FOUND'
                    then 1
                    else 0
                end)
        * 1.0
        / count (case when i.date = j.date
                      then 1
                      else 0
                 end)
        ) *100
       ) as percentage
from  author_article_log as i, author_article_log as j
group by i.date, j.date
order by percentage desc;

运行此查询不会返回结果，也不会出现任何错误，有人可以告诉我为什么会这样吗？

Answer 1

您不需要自我加入
您需要sum()，而不是count()注意：COUNT(0)等于1
DATE是关键字；最好不要将其用作列名

SELECT zdate,
       100.0 * SUM (CASE WHEN status = '404 NOT FOUND' THEN 1 ELSE 0 END)
        / COUNT(*) AS percentage
FROM  author_article_log
GROUP BY zdate
ORDER BY percentage DESC
        ;

Answer 2

您可以尝试使用WITH子句来过滤您的请求

WITH errors AS (
  SELECT date, COUNT(*) AS nb_errs
  FROM author_article_log
  WHERE status = '404 NOT FOUND'
  GROUP BY date
), total AS (
  SELECT date, COUNT(*) AS nb_queries
  FROM author_article_log
  GROUP BY date
)
SELECT e.date, 100.0 * e.nb_errs / t.nb_queries AS percentage
FROM errors e
JOIN total t ON e.date = t.date
ORDER BY percentage DESC

文档：PostgreSQL: Documentation: 10: 7.8. WITH Queries (Common Table Expressions)

SQL查询未显示任何结果

2 个答案: