计算用户相互汇款的交易表中的余额

Question

我有一个这样设置的事务表：

-- Transactions table
+----+---------+-------+------------------+--------+-----------+
| id | from_id | to_id | transaction_type | amount | card_type |
+----+---------+-------+------------------+--------+-----------+
| 1  | 1       | 1     | deposit          | 90     | debit     |
| 2  | 1       | 2     | transfer         | -60    | debit     |
| 3  | 2       | 2     | deposit          | 10     | debit     |
| 4  | 2       | 2     | deposit          | 20     | credit    |
+----+---------+-------+------------------+--------+-----------+

如果我存入它应该显示一个正值以表明钱已添加到我的帐户中，但如果我进行转帐它应该使用负余额表明钱已从我的帐户中删除。问题是，我想不出一个查询会从用户 1 的转移中将钱添加到用户 2 的账户以产生这样的视图（基于卡类型）：

-- Debit Balance Table
+---------+---------+
| user_id | balance |
+---------+---------+
| 1       | 30      |
| 2       | 70      |
+---------+---------+

-- Credit Balance Table
+---------+---------+
| user_id | balance |
+---------+---------+
| 1       | 0       |
| 2       | 20      |
+---------+---------+

我知道您不能将钱添加到信用帐户，但现在忘记这个逻辑。

Answer 1

对于debit，你可以简单的做条件聚合：

SELECT 
  all_users.user_id, 
  SUM (CASE 
         WHEN t.transaction_type = 'deposit' AND all_users.user_id = t.from_id
           THEN ABS(t.amount) 
         WHEN t.transaction_type = 'transfer' AND all_users.user_id = t.from_id
           THEN -ABS(t.amount)
         WHEN t.transaction_type = 'transfer' AND all_users.user_id = t.to_id
           THEN ABS(t.amount)
         ELSE 0
       END
      ) AS balance 
FROM transactions AS t 
JOIN (
      SELECT from_id AS user_id FROM transactions 
      UNION 
      SELECT to_id FROM transactions
     ) AS all_users 
  ON t.from_id = all_users.user_id OR 
     t.to_id = all_users.user_id 
WHERE t.card_type = 'debit' 
GROUP BY all_users.user_id