find max in self join after multiple joins

Question

i'm trying to find the highest number of interviews from each category (month and city) by joining two different tables and doing a self join in sql

`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`

the above code works that shows a self join after multiple join to compare every event_id for the number of total_interviews, but when i add after where

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

to find the max value, it gives me an error saying there is no such column for table1 and table2.

the reason why i added this is so that i can determine which event_id has the highest number of interviews compared to the rest, but i haven't been able to find out how to do this

Answer 1

Trying to work back from what I think is the source data, before your initial self join, does this give you what you want? This is in sql server.

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

Result is this:

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

Answer 2

You can simply use below query.

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