Question

I have a table with users. Each user has a country. What I want is to get the list of all countries with the numbers of users and the percent/total. What I have so far is:

SELECT
country_id,
COUNT(*) AS total,
((COUNT(*) * 100) / (SELECT COUNT(*) FROM users WHERE cond1 = true AND cond2 = true AND cond3 = true)::decimal) AS percent
FROM users
WHERE cond1 = true AND cond2 = true AND cond3 = true
GROUP BY contry_id

Conditions in both of queries are the same. I tried to do this without a subquery but then I can’t get the total number of users but total per country. Is there a way to do this without a subquery? I’m using PostgreSQL. Any help is highly appreciated.
Thanks in advance

Answer 1

I am not a PostgreSQL user but, the general solution would be to use window functions.

Read up on how to use this at http://developer.postgresql.org/pgdocs/postgres/tutorial-window.html

Best explanation i could use to describe it is: basically it allows you to do a group by on one field without the group by clause.

I believe this might do the trick:

SELECT 
    country_id, 
    COUNT(*) OVER (country_id) 
    ((((COUNT(*) OVER (country_id)) * 100) / COUNT(*) OVER () )::decimal) as percent
FROM 
    users
WHERE
    cond1 = true AND cond2 = true AND cond3 = true