mysql select語句中的子查詢

Question

我正在嘗試編寫一個查詢，其中按用戶使用的促銷代碼對用戶進行排序，並告訴我這些用戶中有多少擁有免費計划，有多少擁有付費計划。 這是我的嘗試。

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

這是行不通的，但是我不確定要進行哪些更改才能使其正常工作。

Answer 1

通過功能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