How to calculate percent?

Question

Could you help me to calculate percent of users, which made payments? I\'ve got two tables:

activity
user_id  login_time
201      01.01.2017
202      01.01.2         


        

Answer 1

If you want the ratio of users who have made payments to those with activity, just summarize each table individually:

select p.cnt / a.cnt
from (select count(distinct user_id) as cnt from activity a) a cross join
     (select count(distinct user_id) as cnt from payment) p;

EDIT:

You need a table with all dates in the range. That is the biggest problem.

Then I would recommend:

SELECT d.dte,
       ( ( SELECT COUNT(DISTINCT p.user_id)
           FROM payments p
           WHERE p.payment_date >= d.dte and p.payment_date < d.dte + INTERVAL 1 DAY
          ) /
          NULLIF( (SELECT COUNT(DISTINCT a.user_id)
                   FROM activity a
                   WHERE a.login_time >= d.dte and p.login_time < d.dte + INTERVAL 1 DAY
                  ), 0
                 ) as ratio
FROM (SELECT date('2017-01-01') dte UNION ALL
      SELECT date('2017-01-02') dte UNION ALL
      SELECT date('2017-01-03') dte UNION ALL
      SELECT date('2017-01-04') dte UNION ALL
      SELECT date('2017-01-05') dte 
     ) d;

Notes:

• This returns NULL on days where there is no activity. That makes more sense to me than 0.
• This uses logic on the dates that works for both dates and date/time values.
• The logic for dates can make use of an index, which can be important for this type of query.
• I don't recommend using LEFT JOINs. That will multiply the data which can make the query expensive.