Question

我们需要找出XYZ公司（来自项目）每个项目的总成本。总成本被视为发票明细表中（单位价格*数量）的总和。

要查找每个项目的总成本，您需要在查询中加入3个表：XYZ_PROJECTS使用XYZ_INVOICES（使用PROJECT_NUMBER）和XYZ_INVOICES使用XYZ_INVOICE_DETAILS（使用INVOICE_NUMBER）。
转到SQLWorkshopSQL命令。编写并执行“选择”查询以从XYZ_INVOICE_DETAILS中选择项目编号，项目名称来自XYZ_PROJECTS，sum（c.qty * c.Unit_price）。（您需要在查询结尾添加“group by project_number，project_name”，因为使用了SUM聚合函数）。运行查询。您的屏幕应如下所示

我用它来加入表，但我不知道如何同时加入3个表。

 select *
 from XYZ_PROJECTS c 
 join XYZ_INVOICES do on c.PROJECT_NUMBER = do.PROJECT_NUMBER

 select * 
 from XYZ_INVOICES i 
 join XYZ_INVOICE_DETAILS do on i.INVOICE_NUMBER = do.INVOICE_NUMBER

也许我做错了。请帮助我。

Answer 1

select c.project_number, c.project_name, sum(do.qty * do.Unit_price)
from XYZ_PROJECTS c 
join XYZ_INVOICES i
    on c.PROJECT_NUMBER = i.PROJECT_NUMBER
join XYZ_INVOICE_DETAILS do 
    on i.INVOICE_NUMBER = do.INVOICE_NUMBER
group by c.project_number, c.project_name

如果您需要包含尚无任何发票的零费用项目，请使用left outer join保留XYZ_PROJECTS中的所有行：

select c.project_number, c.project_name, sum(do.qty * do.Unit_price)
from XYZ_PROJECTS c 
left join XYZ_INVOICES i 
    on c.PROJECT_NUMBER = i.PROJECT_NUMBER
left join XYZ_INVOICE_DETAILS do 
    on i.INVOICE_NUMBER = do.INVOICE_NUMBER
group by c.project_number, c.project_name

加入3表查找总费用

1 个答案: