How to calculate max, min and average in postgresql

Question

I want to separate jobs with color based on conversion of what I did as follow:

select count(ap.id), 
       (count(ap.id)/cast(SUM(j.views) as float) * 100) as conversion,
       j.company_id 
  from applications ap 
          right join jobs j 
            on ap.job_id = j.id 
 where j.company_id = 61805
 group by j.id

if conversion column is greater than 75% of total average of that result, I want to create new alias column and value will be green . if conversion column is between 35% and 75%, column value will be yellow and less than 35%, column value will be red .

Is can be possible do in postgres as above query I've mentioned? Thanks in advance.

Answer 1

Window functions are your friend:

SELECT count,
       conversion,
       CASE
          WHEN conversion > avg_conv * 0.75
          THEN 'green'
          WHEN conversion < avg_conv * 0.35
          THEN 'red'
          ELSE 'yellow'
       END AS color,
       company_id
FROM (SELECT count,
             conversion,
             avg(conversion) OVER () AS avg_conv,
             company_id
      FROM (SELECT count(ap.id), 
                   (count(ap.id)/cast(SUM(j.views) as float) * 100) AS conversion,
                   j.company_id 
            FROM applications ap 
               RIGHT JOIN jobs j 
                  ON ap.job_id = j.id 
            WHERE j.company_id = 61805
            GROUP BY j.company_id
           ) with_avg
     ) with_color;

(untested)