计算 PostgreSQL 中的帐户余额历史记录

Question

我正在尝试使用 SQL 获取帐户的余额历史记录。 我在PostgreSQL中的表如下所示：

   id  sender_id    recipient_id           amount_money
   --- -----------  ---------------------- -----------------
   1   1            2                      60.00
   2   1            2                      15.00
   3   2            1                      35.00

所以 ID 号为 2 的用户目前在他的帐户中有 40 美元。 我想使用 sql 得到这个结果：

[60, 75, 40]

是否可以在 postgres 中使用 sql 做这样的事情？

Answer 1

要获得滚动余额，您可以根据id是收件人还是SUM对金额（最多并包括当前行）求和：

SELECT id, sender_id, recipient_id, amount_money,
       SUM(CASE WHEN recipient_id = 2 THEN amount_money
                WHEN sender_id = 2 THEN -amount_money
           END) OVER (ORDER BY id) AS balance
FROM transactions

Output：

id  sender_id   recipient_id    amount_money    balance
1   1           2               60.00           60.00
2   1           2               15.00           75.00
3   2           1               35.00           40.00

如果你想要一个数组，你可以使用array_agg和上面的查询作为派生表：

SELECT array_agg(balance)
FROM (
  SELECT SUM(CASE WHEN recipient_id = 2 THEN amount_money
                  WHEN sender_id = 2 THEN -amount_money
             END) OVER (ORDER BY id) AS balance
  FROM transactions
) t

Output：

[60,75,40]

dbfiddle 上的演示

如果您想更复杂并支持多个帐户的余额，则需要将初始数据拆分为帐户 id，当 id 为接收者时添加，当发送者时减去。 您可以使用CTE生成适当的数据：

WITH trans AS (
  SELECT id, sender_id AS account_id, -amount_money AS amount
  FROM transactions
  UNION ALL
  SELECT id, recipient_id AS account_id, amount_money AS amount
  FROM transactions
),
balances AS (
  SELECT id, account_id, ABS(amount),
         SUM(amount) OVER (PARTITION BY account_id ORDER BY id) AS balance
  FROM trans
)
SELECT account_id, ARRAY_AGG(balance) AS bal_array
FROM balances
GROUP BY account_id

Output：

account_id  bal_array
1           [-60,-75,-40]
2           [60,75,40]

dbfiddle 上的演示