Oracle-不是单组分组功能

Question

For the following sql command

select h.hacker_id
    ,h.name
    ,challenges_created
from hackers h
inner join (
    select hacker_id
        ,count(*) as challenges_created /* line 1 */
    from challenges
    group by hacker_id
    order by 2 desc
    ) tmp on h.hacker_id = tmp.hacker_id
order by challenges_created desc
    ,h.hacker_id;

so far so good but

As soon as I try to add max(count(*)) as maximum to the line 1 it give error as:

Not a single-group group function

This is the code for which it gives error :

select h.hacker_id
    ,h.name
    ,challenges_created
from hackers h
inner join (
    select hacker_id
        ,count(*) as challenges_created
        ,max(count(*)) as maximum
    from challenges
    group by hacker_id
    ) tmp on h.hacker_id = tmp.hacker_id
order by challenges_created desc
    ,h.hacker_id;

I am basically interested in getting the maximum count ie maximum number of challenges created so far.

I am new to sql, kindly help and oblige. Thanks in advance. And yes, of course! I know many such question have been asked in recent past but none matches my situation which is why I am asking it again.

Answer 1

Try this:

with x as (
  select h.hacker_id, h.name, count(*) challenges_created 
  from hackers h 
  inner join challenges on h.hacker_id = challenges.hacker_id
  group by h.hacker_id, h.name
)
select x.*, 
       (select max(challenges_created) from x) as "max"
from x
order by challenges_created desc, hacker_id;