-- 限制查询结果数量
-- 查询浏览量最高的前5个商品
select item_id,sum(behavior_type='pv') as 浏览量
from userbehavior
group by item_id
order by 浏览量 desc
limit 5;


select item_id,sum(behavior_type='pv') as 浏览量
from userbehavior
group by item_id
order by 浏览量 desc
limit 0,5;