sql查询:联合查询

--使用Northwind
--连接查询
--内连接(Inner Join)
select  p.* from  Products p inner join [Order Details] o on p.ProductID=o.ProductID 
go
select  p.*,c.* from  Products p inner join Categories c on c.CategoryID=p.CategoryID 
go

--1、左外连接
select  p.*,c.* from Categories c  left outer join Products p on p.CategoryID=c.CategoryID  order by p.ProductID
--2、右外连接
select  p.*,c.* from Categories c  right outer join Products p on p.CategoryID=c.CategoryID  order by p.ProductID
--3、全外连接
select  p.*,c.* from Categories c  full outer join Products p on p.CategoryID=c.CategoryID  order by p.ProductID
--子查询

--1、使用比较运算符的子查询
select * from Products  where unitprice>(select avg(unitprice) from Products)
--2、使用IN的子查询
select * from Products where categoryID in (select categoryID from categories)
--3、使用some和any的子查询

select * from Products  where unitprice<some(select avg(unitprice) from Products)



--4、使用All的子查询
select * from Products  where unitprice<>All(select avg(unitprice) from Products)

--5、使用Exists的子查询
select * from Products where  exists (select * from categories where categories.categoryID=Products.categoryID and categories.categoryID=2)