嘗試基於另一個表獲取結果-WHERE中不允許使用聚合函數

Question

我正在嘗試編寫一個查詢，該查詢將根據他們從另一張表中獲得的捐款總額來選擇所有用戶，並按捐款總額進行排序。 但是我遇到了錯誤。 我正在使用postgres，但我想同樣適用於mysqql。

ERROR:  aggregate functions are not allowed in WHERE
LINE 8:  sum(donations.donation) = 400
         ^

用戶表

id |   username   |
1     Larry Page
2     Sergey Brin

捐款表

id | user_id | donation |     date
1      1         100       2019-02-12
2      1         200       2019-02-13
3      2         500       2019-01-15
4      1         100       2019-04-10

這是我的查詢

select
    users.username, sum(donations.donation) as donation_sum
from
    users
inner join donations
    on users.id = donations.user_id
where
    sum(donations.donation) = 400
and
    donations.date between '2019-01-01' and '2019-12-31'
order by
    donation_sum

我期待結果是這樣

username    |  donation_sum
Larry Page        400

Answer 1

要過濾聚合結果，必須使用關鍵字HAVING ：

select
    users.username, sum(donations.donation) as donation_sum
from
    users
inner join donations
    on users.id = donations.user_id
where
    donations.date between '2019-01-01' and '2019-12-31'
group by
    users.username
having
    sum(donations.donation) = 400
order by
    donation_sum