Question

我想使用原始sql计算帐户余额，而无需额外的应用程序逻辑。事务架构包括amount，from_account_id和to_account_id

我的查询是

SELECT SUM(tdebit.amount) - SUM(tcredit.amount) as balance
FROM accounts as a
INNER JOIN transactions as tdebit ON a.id = tdebit.to_account_id
INNER JOIN transactions as tcredit ON a.id = tcredit.from_account_id
WHERE a.id = $1 AND tdebit.succeed = true AND tcredit.succeed = true

它不能像我预期的那样工作 - 结果是错误的，但如果我加入交易只有一次它正常工作，例如只需借记金额就可以了

SELECT SUM(tdebit.amount) as debit
FROM accounts as a
INNER JOIN transactions as tdebit ON a.id = tdebit.to_account_id
WHERE a.id = $1 AND tdebit.succeed = true

我的余额查询中错过了什么？

http://sqlfiddle.com/#!15/b5565/1

Answer 1

您基本上是在计算tdebits和tcredits之间的叉积，即tdebits中您正迭代tcredits中所有行的每一行。也没有理由加入accounts（除非to_account_id和from_account_id不是外键）。

您只需要对交易进行一次通过，您只需要知道金额是信用卡还是借记卡。

SELECT SUM(CASE WHEN t.to_account_id = $1 THEN t.amount ELSE -t.amount END) AS amount
FROM transactions AS t
WHERE (t.to_account_id = $1 OR t.from_account_id = $1)
  AND t.succeed = true

如果帐户可以转移到自身，请添加t.to_account_id <> t.from_account_id。

Answer 2

在进行连接之前进行聚合，如果您想要所有帐户的值：

select a.*, coalesce(tdebit.debit, 0) - coalesce(tcredit.credit, 0)
from accounts a left join
     (select t.to_account_id, sum(t.amount) as debit
      from transactions t
      group by t.to_account_id
     ) tdebit
     on a.id = tdebit.to_account_id left join
     (select t.from_account_id, sum(t.amount) as credit
      from transactions t
      group by t.from_account_id
     ) tcredit
     on a.id = tcredit.from_account_id;

用于计算帐户余额的SQL查询

2 个答案: