1.背景要求：统计消费金额大于1000元，800到100元，500到800元，500元以下的人数。
select
count(case when ifnull(total_money,0)>=1000 then a.user_id end) as '大于100'，
count(case when ifnull(total_money,0)>=800 and ifnull（total_money,0）<1000 then a.user_id end) as '大于100'，
count(case when ifnull(total_money,0)>=500 and total_money<=800 then a.user_id end) as '大于800小于1000'，
count(case when ifnull(total_money,0)>=1000 then a.user_id end) as '大于500 小于800‘，
count(case when ifnull(total_money,0)<=500 then a.user_id end) as '小于500‘
from a