mysql select语句中的子查询

Question

我正在尝试编写一个查询，其中按用户使用的促销代码对用户进行排序，并告诉我这些用户中有多少拥有免费计划，有多少拥有付费计划。 这是我的尝试。

select count(refer) as promo, (count(plan)
    from users
    where plan = 'free'
) as free, (count(plan)
    from users
    where plan <> 'free'
) as pay from users
where refer <> ''
group by refer

这是行不通的，但是我不确定要进行哪些更改才能使其正常工作。

Answer 1

通过功能CASE可以

select count(refer) as promo, 
count(case when plan = 'free' then 1 end) as free
count(case when plan <> 'free' then 1 end) as pay
from users
where refer <> ''
group by refer