如何计算 SQL 中 1 个字段中每个条件的 SUM？

Question

我又回来了，哈哈，我正在尝试计算以下内容：

找出有多少用户在过去 30 天内至少有一次余额超过 2000 英镑，因此应该通过贷记借记来获取每个用户的余额。

我已附上数据库

我尝试了以下，基本上是自连接，但输出缺少值。

SELECT user_id, (credit_amount - debit_amount) AS balance
FROM (SELECT A.user_id, A.type, B.type, A.amount AS debit_amount, B.amount AS credit_amount
      FROM public.transaction A, public.transaction B
      WHERE A.user_id = B.user_id
      AND a.type LIKE 'debit'
      AND b.type LIKE 'credit'
      AND A.created_at >= CURRENT_DATE - INTERVAL '30 days'
      AND A.created_at <= CURRENT_DATE) AS table_1
WHERE (credit_amount - debit_amount) > 2000
;

但是，user_id 3 由于在时间间隔内没有信用而被跳过，并且一些值被遗漏了。任何帮助都会很好，谢谢。

Answer 1

SELECT user_id, 
   c.credit_amount - b.debit_amount AS balance
FROM public.transaction a

JOIN (SELECT 
    user_id, type, amount AS debit_amount, 
  FROM public.transaction 
  where a.type LIKE 'debit') b on a.user_id = b.user_id

JOIN (SELECT
  user_id, type, amount AS credit_amount
  FROM public.transaction 
  where type LIKE 'credit') c on a.user_id = c.user_id

WHERE a.created_at >= CURRENT_DATE - INTERVAL '30 days'
AND a.created_at <= CURRENT_DATE) AS table_1
AND (c.credit_amount - b.debit_amount) > 2000
GROUP BY a.user_id;

Answer 2

找出过去 30 天内有多少用户至少有一次的余额超过了 2000 英镑，

您可以使用窗口函数计算每个用户在此期间的运行余额。然后，您只需要统计运行余额曾经超过阈值的不同用户：

select count(distinct user_id)  no_users
from (
    select 
        user_id,
        sum(case when type = 'credit' then amount else -amount end) 
            over(partition by user_id order by created_at) balance
    from transaction
    where created_at >= current_date - interval '30' day and created_at < current_date
) t
where balance > 2000

Answer 3

使用条件聚合：

select user_id,
       (sum(amount) filter (where type = 'credit') -
        coalesce(sum(amount) filter (where type = 'debit'), 0)
       )
from public.transaction t
where t.created_at >= CURRENT_DATE - INTERVAL '30 days' and
      t.created_at < CURRENT_DATE
group by user_id;