Postgres recursive CTE or crosstab function - sql

Question

I try to generate some user statistics from a table that includes logging information.
**TABLE users**
user_id | user_name
-------------------
1 | julia
2 | bob
3 | sebastian
**TABLE logs**
user_id | action | timepoint
------------------------------------
1 | create_quote | 2015-01-01
1 | send_quote | 2015-02-03
1 | create_quote | 2015-02-02
1 | start_job | 2015-01-15
2 | start_job | 2015-02-23
2 | send_quote | 2015-03-04
2 | start_job | 2014-12-02
My desired output is the following table
user_id | username | create_quote | send_quote | start_job
-----------------------------------------------------------
1 | julia |2 | 1 | 1
2 | bob |0 | 1 | 1
3 | sebastian |0 | 0 | 0
It includes all users (even if there was nothing logged), but only the actions between date '2015-01-01' and '2015-05-31'. Actions are counted/grouped by action type and user.
The SQL statement could look someting like
SELECT * FROM myfunction() WHERE to_char(timepoint, 'YY/MM') BETWEEN '15/01' AND '15/05';
Do you have any idea how to manage this? I've been trying around with CTEs and recursion as well as with the crosstab function but could not find any solution.

Answer 1

I think the crosstab function would be a lot more elegant, but in the case that you don't have the extension loaded or, like me, struggle with the syntax, this is a kind of clumsy, brute-force way you could do it:
CREATE OR REPLACE FUNCTION get_stats(
from_date date,
thru_date date)
RETURNS table (
user_id integer,
username text,
create_quote bigint,
send_quote bigint,
start_job bigint
) AS
$BODY$
select
l.user_id, u.username,
sum (case when action = 'create_quote' then 1 else 0 end) as create_quote,
sum (case when action = 'send_quote' then 1 else 0 end) as send_quote,
sum (case when action = 'start_job' then 1 else 0 end) as start_job
from
logs l
join users u on l.user_id = u.user_id
where
l.timepoint between from_date and thru_date
group by
l.user_id, u.username
$BODY$
LANGUAGE sql VOLATILE
COST 100
ROWS 1000;
And then your query would be:
select * from get_stats('2015-01-01', '2015-05-31')
Personally, I would skip the function and just create it as a query, but it's conceivable there are reasons where you would want the function wrapper.
-- EDIT --
Based on an attempted edit, I see you may be okay with a query. Also, you wanted users that have no entries.
With all of that in mind, I think this might work:
select
u.user_id, u.username,
sum (case when action = 'create_quote' then 1 else 0 end) as create_quote,
sum (case when action = 'send_quote' then 1 else 0 end) as send_quote,
sum (case when action = 'start_job' then 1 else 0 end) as start_job
from
users u
left join logs l on
l.user_id = u.user_id and
l.timepoint between '2015-01-01' and '2015-05-31'
group by
u.user_id, u.username