mysql 连接三个表

Question

与 another question 类似的问题，除了我的三个 table 是分层的，而不是并排的两个 table。

我的table是

我的顶级客户table

id | name
1  | alan
2  | bob
3  | charlie

我的二级发票table

id | client_id | paid
1  | 1         | 0
2  | 1         | 1
3  | 2         | 1

还有我的 3 级服务 table

id | invoice_id | amount
1  | 1          | 5.00
2  | 1          | 10.00
3  | 2          | 5.00
4  | 3          | 10.00

我想要的结果是

id | name    | amount_owing | amount_paid
1  | alan    | 15.00        | 5.00
2  | bob     | null         | 10.00
3  | charlie | null         | null

我可以得到一些不考虑他们是否支付的东西

SELECT
    clients.email,
    jnt.*
FROM clients
LEFT JOIN (
    SELECT 
        invoices.client_id,
        SUM(amount) AS invoice_total_paid
    FROM
        invoices,
        services
    WHERE 
        invoices.id = services.invoice_id 
    GROUP BY
        invoices.client_id
) AS jnt ON clients.id = jnt.client_id

这给了我

id | name    | client_id | invoice_total
1  | alan    | 1         | 20.00
2  | bob     | 2         | 10.00
3  | charlie | 3         | null

但它不区分发票是否已支付（以及随后的支付和欠款总额）。非常感谢任何帮助

Answer 1

您可以使用条件聚合获得预期结果：

SELECT c.id, c.name,
       SUM(CASE WHEN i.paid = 0 THEN s.amount ELSE 0 END) AS amount_owing,
       SUM(CASE WHEN i.paid = 1 THEN s.amount ELSE 0 END) AS amount_paid
FROM clients AS c
LEFT JOIN invoices AS i ON c.id = i.client_id
LEFT JOIN services AS s ON i.id = s.invoice_id
GROUP BY c.id, c.name

Demo here

Answer 2

你需要这样的东西

...
SUM(IF(paid=1,amount,0)) AS amount_paid,
SUM(IF(paid=0,0,amount)) AS amount_owning
...

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