使用mysql

Question

我想制作另一个sum数组（来自count）。并计算旁边的百分比。所以我写道：

select vwr_cntry, COUNT(vwr_id) as count1 from viewer_log
where not vwr_cntry = ''
group by vwr_cntry

Union all

select 'SUM'
vwr_cntry, COUNT(count1)//cannot count the 'count1'

from viewer_log
order by count desc
limit 5

这个想法是列出前5个访问者国家并计算每个国家/地区的百分比（vwr_cntry）。我期待这样的事情：

+---------------+---------+-----+
|   Country     |count    |  %  |
+---------------+---------+-----+
|Thailand       |2314     |     |
+---------------+---------+-----+
|United States  |957      |     |
+---------------+---------+-----+
|Japan          |645      |     |
+---------------+---------+-----+
|United Kingdom |70       |     |
+---------------+---------+-----+
|China          |52       |     |
+---------------+---------+-----+

但它会抛出错误：'字段列表'中的未知列'count'

Answer 1

这样的事情应该有效：

SELECT
    vwr_cntry,
    COUNT(*) AS cntry_cnt,
    100.0 * COUNT(*) / (SELECT COUNT(*) FROM viewer_log) AS pct
FROM viewer_log
GROUP BY vwr_cntry
ORDER BY COUNT(*) DESC
LIMIT 5

这只是一个简单的GROUP BY查询。它使用非相关子查询来查找总行数，用于计算百分比。

Answer 2

我首先进入前5个国家，例如：

SELECT vwr_cntry, COUNT(vwr_id) AS 'counts'
FROM viewer_log
GROUP BY vwr_cntry
ORDER BY COUNT(vwr_id) DESC LIMIT 5;

然后，将其包装到另一个查询中以计算sum，e.h。：

SELECT a.vwr_cntry, a.counts, SUM(a.counts) as 'sums'
FROM (
  SELECT vwr_cntry, COUNT(vwr_id) AS 'counts'
  FROM viewer_log
  GROUP BY vwr_cntry
  ORDER BY COUNT(vwr_id) DESC LIMIT 5
) a;

然后，添加公式来计算百分比，例如：

SELECT b.vwr_cntry, b.counts, b.sums, (b.counts/b.sums)*100 AS 'percentage'
FROM (
  SELECT a.vwr_cntry, a.counts, SUM(a.counts) as 'sums'
  FROM (
    SELECT vwr_cntry, COUNT(vwr_id) AS 'counts'
    FROM viewer_log
    GROUP BY vwr_cntry
    ORDER BY COUNT(vwr_id) DESC LIMIT 5
  ) a
) b;