在多個連接后查找自連接中的最大值

Question

我想通過加入兩個不同的表並在sql中自我加入來嘗試從每個類別（月份和城市）中找到最多的訪談次數

`select distinct table1.event_id, table1.month, table1.city

from

(SELECT event_id, count(*) as total_interviews, month, city
FROM company, events
where company.interviewee_id = events.interviewee_id
GROUP BY event_id, month, city) as table1,

(SELECT event_id, count(*) as total_interviews, month, city
FROM company, events
where company.interviewee_id = events.interviewee_id
GROUP BY event_id, month, city) as table2 

WHERE table1.event_id <> table2.event_id
AND table1.month = table2.month
AND table1.city = table2.city`

上面的代碼工作，顯示多個連接后的自連接，以比較每個event_id的total_interviews數量，但當我添加后，在哪里

AND table1.total_interviews > all (select table2.total_interviews FROM table2 WHERE table2.event_id <> table1.event_id) 

為了找到最大值，它給出了一個錯誤，表示table1和table2沒有這樣的列。

之所以我加上這個，是因為我可以確定哪個event_id的訪談次數與其他次數相比最多，但我無法找到如何做到這一點

Answer 1

在您最初的自我加入之前，嘗試從我認為的源數據開始工作，這會給您提供您想要的嗎？ 這是在sql server中。

declare @i table(id int, n int, m varchar(30), city varchar(2))
insert @i values (1,4,'Jan','SF')
,(2,5,'Feb','NY')
,(3,6,'Mar','LA')
,(4,3,'Jan','SF')
,(5,2,'Feb','NY')
,(6,1,'Mar','LA')

;with cte as (
    select *, row_number() over(partition by m,city order by n desc) roworder 
    from @i
)
select id,m,city from cte 
where roworder=1 
order by id

結果如下：

id  m   city
1   Jan SF
2   Feb NY
3   Mar LA

Answer 2

您可以簡單地使用以下查詢。

SELECT * FROM (
    SELECT EventID,total_interviews, Month, City, row_number() over(partition by event_ID,month, City order by total_interviews DESC) as RN
    FROM (
       SELECT Company.event_id, count(*) as total_interviews, Events.month, Events.city, 
       FROM company, events
       where company.interviewee_id = events.interviewee_id
       GROUP BY Company.event_id, Events.month, Events.city 
       ) A
    ) B where RN = 1