mysql - 如何直接从 MySQL 查询中获取两个总和的百分比？

Question

我首先使用以下查询计算数据库中男性和女性的百分比：

SELECT sum(case when `gender` = 'M' then 1 else 0 end) as male
     , sum(case when `gender` = 'F' then 1 else 0 end) as female
FROM userinfo 
WHERE id in (10,1,5)

然后在php中我计算百分比。但我想知道，有没有办法直接从查询中获取百分比？

Answer 1

SELECT sum(case when `gender` = 'M' then 1 else 0 end) as male
     , 100*sum(case when `gender` = 'M' then 1 else 0 end)/count(*) as malepct
     , sum(case when `gender` = 'F' then 1 else 0 end) as female
     , 100*sum(case when `gender` = 'F' then 1 else 0 end)/count(*) as femalepct
FROM userinfo 
WHERE id in (10,1,5)

...假设您没有在空行集上运行它（除以零）

如果您想用 -1 替换无效（除以零）值，请使用

if(ifnull(count(*),0)>0,100*sum(case when `gender` = 'M' then 1 else 0 end)/count(*),-1) as malepct