Question

我有3个表：Book，Invoice，Download最后两个有Book的外键的地方。我需要知道每本书的成功发票和下载数量。为了得到结果，我有2个查询。第一个显示每本书的编号发票：

select b.Title, sum(i.price)
from Book b, Invoice i
where i.BookId = b.Id and i.State = 'successful'
group by b.Title

最后一个显示每本书的下载次数：

select b.Title, count(1)
from Book b, Download d 
where d.BookId = b.Id and d.State = 'successful'
group by b.FarsiTitle

我希望将结果看作一个表，因此我有3列：

book_title，invoice_count，download_count

怎么可能？

Answer 1

我认为最简单的方法是相关子查询：

blog.com/project

如果您想使用project.com，则需要在 select b.*, (select count(*) from invoice i where i.BookId = b.Id and i.State = 'successful' ) as num_invoices, (select count(*) from download d where d.BookId = b.Id and d.State = 'successful' ) as numdownloads from book b;之前汇总以获得正确的计数。

编辑：

在SQL Server中，您可以使用JOIN

JOIN

这与相关子查询非常相似，但允许您进行多次计算。

Answer 2

简单的联合一切都很好，如下所示：

select b.Title, sum(i.price)
from Book b join Invoice i
on i.BookId = b.Id and i.State = 'successful'
group by b.Title

UNION ALL

select b.Title, count(1)
from Book b join Download d 
on d.BookId = b.Id and d.State = 'successful'
group by b.FarsiTitle

合并两个连接的结果

2 个答案: