大家好，我是考100分的小小码 ，祝大家学习进步，加薪顺利呀。今天说一说sql分组统计“group by”,希望您对编程的造诣更进一步.
准备数据
先准备数据，数据如图所示： 
按app字段分组
select
fun(logs.id) as c, -- fun表示聚合函数
logs.app
from public.logs as logs
group by logs.app;
代码100分
计数 count
代码100分select
count(logs.id) as c,
logs.app
from public.logs as logs
group by logs.app
order by c desc
limit 10;
求和 sum
select
sum(logs.packets) as s,
logs.app
from public.logs as logs
group by logs.app
order by s desc
limit 10;
求均值 avg
代码100分select
avg(logs.packets) as s,
logs.app
from public.logs as logs
group by logs.app
order by s desc
limit 10;
取最大值 max
select
max(logs.packets) as s,
logs.app
from public.logs as logs
group by logs.app
order by s desc
limit 10;
取最小值 max
select
min(logs.packets) as s,
logs.app
from public.logs as logs
group by logs.app
order by s desc
limit 10;
取平均值大于11710, having
select
avg(logs.packets) as s,
logs.app
from public.logs as logs
group by logs.app
having avg(logs.packets) > 11710
order by s desc
limit 10;
大小写 upper 和 lower
select upper(logs.d_region), lower(logs.s_region)
from public.logs as logs
limit 10;
字符串长度
select length(logs.d_region) as length_of_region
from public.logs as logs
limit 10;
取平均值大于11710，并且四舍五入 round
select
round(avg(logs.packets), 2) as s,
logs.app,
now() as date
from public.logs as logs
group by logs.app
HAVING avg(logs.packets) > 11710
order by s desc
limit 10;
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