SQL嵌套请求

Question

我有 3 个表格:

1. transaction - 关于用户余额变化的一般信息。 主键:transaction_id。
2. bet_transactions - 关于投注的特殊信息，外键:transaction_id。
3. win_transaction - 与 bet_transactions 相同，但包含 wins。

我想获得所有投注和获胜的总和。 我想到了这个:

select
    u.username as username,
    u.balance as balance,
    sum(bt.amount) as bet_sum,
    sum(wt.amount) as win_sum
from
    users u,
    (
        select 
            t.*
        from 
            transactions t,
            bet_transactions b
        where 
            t.transaction_id = b.transaction_id
    ) bt,
    (
        select 
            t.*
        from 
            transactions t,
            win_transactions w
        where 
            t.transaction_id = w.transaction_id
    ) wt
where
    u.username = bt.username and
    u.username = wt.username
group by
    u.username

它不能正常工作:我总是只得到一行并且总和不正确。 但是，如果我像这样删除其中一个嵌套部分，它就会开始按预期工作。我做错了什么？

select
    u.username as username,
    u.balance as balance,
    sum(bt.amount) as bet_sum
from
    users u,
    (
        select 
            t.*
        from 
            transactions t,
            bet_transactions b
        where 
            t.transaction_id = b.transaction_id
    ) bt
where
    u.username = bt.username
group by
    u.username

Answer 1

将聚合函数和分组依据移动到嵌套子查询中，如下所示:

select
    u.username as username,
    u.balance as balance,
    bt.bet_sum,
    wt.win_sum
from
    users u
    left outer join 
    (
        select 
            t.username, sum(b.amount) as bet_sum
        from 
            transactions t,
            bet_transactions b
        where 
            t.transaction_id = b.transaction_id
        group by
            t.username
    ) bt
       on u.username = bt.username
    left outer join
    (
        select 
            t.username, sum(w.amount) as win_sum
        from 
            transactions t,
            win_transactions w
        where 
            t.transaction_id = w.transaction_id
        group by
            t.username
    ) wt
        on u.username = wt.username

使用 CTE 更具可读性:

WITH 
bt as 
     (
        select 
            t.username, sum(b.amount) as bet_sum
        from 
            transactions t,
            bet_transactions b
        where 
            t.transaction_id = b.transaction_id
        group by
            t.username
    ),
wt as
    (
        select 
            t.username, sum(w.amount) as win_sum
        from 
            transactions t,
            win_transactions w
        where 
            t.transaction_id = w.transaction_id
        group by
            t.username
    ) 
select
    u.username as username,
    u.balance as balance,
    bt.bet_sum,
    wt.win_sum
from
    users u
    left outer join bt
       on u.username = bt.username
    left outer join wt
        on u.username = wt.username

已编辑:

我切换到正确的 ANSI 连接语法，也切换到外部连接和 CTE。谢谢@ThorstenKettner关于建议。