mysql - 15天的Sql From hackerrank

Question

我无法理解代码中这一行的用法，有人可以解释一下这个问题或提供一些不同的方法来解决这个问题

问题链接:https://www.hackerrank.com/challenges/15-days-of-learning-sql

代码:

select 
    submission_date ,    
    (    SELECT COUNT(distinct hacker_id)  
         FROM Submissions s2  
         WHERE s2.submission_date = s1.submission_date 
               AND (  SELECT COUNT(distinct s3.submission_date) 
                         FROM      Submissions s3 
                         WHERE 
                           s3.hacker_id = s2.hacker_id 
                           AND s3.submission_date < s1.submission_date
                   ) = dateDIFF(s1.submission_date , '2016-03-01')) 
    , (   select hacker_id  
          from submissions s2 
          where s2.submission_date = s1.submission_date 
          group by hacker_id 
         order by count(submission_id) desc , hacker_id limit 1
       ) as shit
    ,  (   select name 
           from hackers where hacker_id = shit
       )
FROM  
(    select distinct submission_date 
     from submissions) s1
group by submission_date

无法理解为什么他们使用这部分代码中的这一行:

 (s3.submission_date < s1.submission_date) = dateDIFF(s1.submission_date , '2016-03-01')) 

Answer 1

CREATE TABLE #max_submissions (
    submission_date date,
    hacker_id integer,
    submission_count integer,
    ordering_row integer
)

insert into #max_submissions 
select 
    submission_date, 
    hacker_id, 
    submission_count, 
    row_number() over(partition by submission_date order by submission_count desc, hacker_id) as ordering_row
from (
    select submission_date, 
            hacker_id,
            count(hacker_id) as submission_count
    from submissions
    group by submission_date, hacker_id
) tbl_submission_count 

CREATE TABLE #hacker_counts (
    submission_date date,
    hacker_count integer
)

insert into #hacker_counts
select tbl.submission_date, 
        COUNT(distinct tbl.hacker_id) as cc 
from (
    select *,
            (case when (
                            (select count(*) 
                                from (select distinct * 
                                        from (select s1.hacker_id, 
                                                    s1.submission_date 
                                                from Submissions s1 
                                                where s1.hacker_id = s.hacker_id and
                                                (s1.submission_date >= '2016-03-01' and 
                                                s1.submission_date <= s.submission_date)) t1 
                                    ) t2 
                            ) >= (DATEDIFF(day, '2016-03-01', s.submission_date) + 1) )
                    then 1
                    else 0
            end) as logic
    from Submissions s
) tbl
where tbl.logic = 1
group by tbl.submission_date



select max_submissions.submission_date, 
    hacker_counts.hacker_count, 
    max_submissions.hacker_id, 
    h.name 
from #max_submissions max_submissions
inner join hackers h on max_submissions.hacker_id = h.hacker_id
left join #hacker_counts hacker_counts on max_submissions.submission_date = hacker_counts.submission_date
where max_submissions.ordering_row = 1
order by max_submissions.submission_date

drop table #max_submissions
drop table #hacker_counts