Get last instance of counted rows - sql

Question

There are two tables jobs and users. users has a 1-to-many relation to jobs.
I want to grab the email of all users who have done 5 or more jobs.
The query below does that. However, how can I also retrieve the date of the last job done by the user.
So the desired output would be:
Email jobs done date of last of job
jack#email.com 5+ 1-20-2015
joe#email.com 5+ 2-20-2015
Query that grabs all emails of users who have done 5+ jobs
select
email
, case
when times_used >= 5
then '5+'
end as times_used
from
(
select
u.id
, u.email as email
, count(*) as times_used
from
jobs j
join users u on
j.user_id = u.id
group by
u.id
)
a
where
times_used >= 5
group by
times_used
, email

Answer 1

You could add a join for another derived table that pulls the last date for each user:
select
b.email,
case when times_used >= 5 then '5+' end as 'jobs done',
b.max_date 'date of last job'
from (
select u.id, count(*) as times_used
from jobs j
join users u on j.user_id = u.id
group by u.id
) a
join (
select u.id, u.email, max(j.date) max_date
from jobs j
join users u on j.user_id = u.id
group by u.id, email
) b on b.id = a.id
where times_used >= 5
But if you only want the email, number of jobs and date of the last job for all users that have 5+ jobs then you the query below should be enough:
select u.id, u.email, max(j.date) max_date
from jobs j
join users u on j.user_id = u.id
group by u.id, u.email
having count(j.id) >= 5
Both queries assume that the jobs table looks like id (pk), user_id, date so you have to adjust according to your actual table definition.

Answer 2

You should try WINDOW function approach, as it can be more efficient:
WITH user_jobs AS (
SELECT
u.id as user_id,
j.id as job_id,
u.email,
ROW_NUMBER() OVER (PARTITION BY u.id ORDER BY j.date DESC) as rn,
ROW_NUMBER() OVER (PARTITION BY u.id ORDER BY j.date) as job_number
FROM
jobs j
join users u ON j.user_id = u.id
)
SELECT
user_id,
job_id,
email,
job_number
FROM user_jobs
WHERE rn = 1 and job_number >= 5