本文介绍了一种使用SQL进行复杂联接操作的方法，通过左外联接将客户表与订单、订单详情及产品表关联，并进一步关联到供应商表，实现了从销售客户角度查询其对应的供应商信息的功能。
select distinct c.companyname as customer,s.companyname as supplier
from sales.customers as c
left outer join
(
sales.orders as o
join
sales.orderdetails as od
on
o.orderid=od.orderid
join
production.products as p
on
p.productid=od.productid
join
production.suppliers as s
on
s.supplierid=p.supplierid
)
on o.custid=c.custid
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