数据表结构
username type num
aaaa 玉米 1212
aaaa 玉米 212
bbb 小麦 2323
bbb ....
只有两种产品 玉米和小麦，玉米价格1.5，小麦价格1.2 求总价值？
with a as( select type,sum(num) as num from foods group by type), b as( select type,(case when type=‘小麦‘ then 1.2 when type=‘玉米‘ then 1.5 end)*num as price from a) select sum(price) as result from b
原文：http://www.cnblogs.com/guwei4037/p/5585473.html