Question

我真的在努力解决这个问题。我有4张桌子（http://oberto.co.nz/db-sql.png）：

Invoice_Payement，Invoice，Client和Calendar。我试图通过按月/年总结Invoice_Payment中的'paid_amount'列来创建报告。

查询需要包括所有月份，即使是那些没有数据的月份
查询需要条件（发票表）：registered_id = [id]

我尝试使用以下查询，但是当'paid_date'没有任何一个月的记录时，该查询就会失败。结果是月份未显示在结果中

我添加了一个Calendar表来解决这个问题但不确定如何保持联接。

SELECT 
   MONTHNAME(Invoice_Payments.date_paid) as month, 
   SUM(Invoice_Payments.paid_amount) AS total
FROM Invoice, Client, Invoice_Payments
WHERE Client.registered_id = 1
AND Client.id = Invoice.client_id
And Invoice.id = Invoice_Payments.invoice_id
AND date_paid IS NOT NULL
GROUP BY YEAR(Invoice_Payments.date_paid), MONTH(Invoice_Payments.date_paid)

请参阅上面的链接，了解我的方案的基本ERD图。

数据库：http://oberto.co.nz/ 预期输出：我下面的当前查询将返回如下内容：

month       total
August      5
September   0
October  196
November  205
December  214
January  229

感谢阅读。我以前发过这个问题，但我觉得我说的很糟糕。

Answer 1

问题显然是你没有进行左连接，所以解决方案可能是重写查询以使用连接语法，您可以在其中指定您想要左连接。像

这样的东西

在client.id = invoice.client_id left join

上从发票左侧加入客户端中选择*

等等

Answer 2

更新：P，这会有效吗？

SELECT YEAR(calendar.date_field) as year,
 MONTHNAME(calendar.date_field) as month,
 SUM(Invoice_Payments.paid_amount) AS total 
FROM calendar
 left outer join invoice_Payments on calendar.date_field = invoice_Payments.date_paid
 left outer join Invoice on invoice_payments.invoice_id = invoice.invoice_id
 left outer join (select * from client where registered_id = 1) as c on c.id = Invoice.client_id
GROUP BY YEAR(calendar.date_field), MONTH(calendar.date_field)

Answer 3

这也可以起作用......

SELECT MONTHNAME(Invoice_Payments.date_paid) as month, SUM(Invoice_Payments.paid_amount) AS total
FROM Client
LEFT OUTER JOIN Invoice ON Client.id = Invoice.client_id
LEFT OUTER JOIN Invoice_Payments ON Invoice.id = Invoice_Payments.invoice_id
WHERE Client.registered_id = 1 AND date_paid IS NOT NULL
GROUP BY YEAR(Invoice_Payments.date_paid), MONTH(Invoice_Payments.date_paid);

mySQL Left加入多个表

3 个答案: