create temporary table aa as 
(select CustomerID as '客户ID',sum(Quantity) as '2017购买数量' from orderinfo 
	where year(OrderDate)='2017'
	and orderinfo.CustomerID in (select distinct CustomerID from orderinfo where year(OrderDate)='2016')
	group by CustomerID);

create temporary table bb as 
(select CustomerID as '客户ID',sum(Quantity) as '2016购买数量' from orderinfo 
	where year(OrderDate)='2016'
	group by CustomerID) ;
	
select aa.客户ID,2016购买数量,2017购买数量 from aa,bb where aa.客户ID=bb.客户ID;