将查询结果中的一列附加到 SQL 中的另一列

Question

我的第一个查询是：

SELECT client.name, client.balance, SUM(payment.amount) AS paid
FROM client, payment
WHERE payment.clientid = client.client_id
GROUP BY client.name, client.balance

这给出了以下结果：

|Name  | Balance | Paid|
|------|---------|-----|
|name1 |5000     |125  |
|name2 |6000     |150  |

我的第二个查询是：

SELECT client.name, client.balance,  SUM(price) AS due
FROM client, reservation, trip, excursion 
WHERE client.client_id = reservation.client_id AND
        trip.tripid = reservation.tripid AND
        trip.exname = excursion.exname
GROUP BY client.name, client.balance

它给出了：

|Name  | Balance | Due |
|------|---------|-----|
|name1 |5000     |250  |
|name2 |6000     |100  |
|name3 |3000     |100  |
|name4 |1000     |100  |

如何合并这两个结果以得到一个包含已付款和到期值的表：

|Name  | Balance | Due | Paid|
|------|---------|-----|-----|
|name1 |5000     |250  |125  |
|name2 |6000     |100  |150  |
|name3 |3000     |100  |     |
|name4 |1000     |100  |     |

Answer 1

获得所需结果的最简单方法是将这两个查询视为“表表达式”并将它们连接起来。

例如，你可以这样做：

select
  x.*,
  y.paid
from (
  SELECT client.name, client.balance,  SUM(price) AS due
  FROM client
  JOIN reservation ON client.client_id = reservation.client_id
  JOIN trip ON trip.tripid = reservation.tripid
  JOIN excursion ON trip.exname = excursion.exname
  GROUP BY client.name, client.balance
) x
left join (
  SELECT client.name, client.balance, SUM(payment.amount) AS paid
  FROM client
  JOIN payment ON payment.clientid = client.client_id
  GROUP BY client.name, client.balance
) y on y.name = x.name

我根据现代标准重新表述了 JOIN。避免使用 80 年代的逗号分隔的 FROM 语法。

现在，我确信有更短的方法可以更简单。

Answer 2

下面的代码 sn-p 应该可以工作

SELECT
    client.name,
    client.balance,
    SUM(price) AS due,
    SUM(payment.amount) AS paid
FROM
    client,
    payment,
    reservation,
    trip,
    excursion
WHERE
    payment.clientid = client.client_id
    AND client.client_id = reservation.client_id
    AND trip.tripid = reservation.tripid
    AND trip.exname = excursion.exname
GROUP BY
    client.name,
    client.balance