Question

A project has many tasks.
A task can be handled by one of many users. For example:

Project    Task      By
-------  --------  ------
  P1        T1       U1
            T2       U2
  P2        T1       U3
            T2       U4
            T3       U5
  P3        T1       U1
            T2       U3
            T3       U5
  P4        T1       U1
            T2       U3

How can I query the count of, the last task in projects handled by users? The output report is expected as:

  Task   By   Count
  ----  ----  -----
   T2    U2     1
   T2    U3     1
   T3    U5     2

UPDATE: (for Deefours’ comment): Here is what I did to get count of last task (but not sure how to get the By column):

self.find_by_sql('select task_id, count(task_id) as "count"
from (
        select task_id
        from (
                select * from tasks order by created_at desc
             )
        tasks_sorted 
        group by project_id
     )
latest_tasks 
group by task_id;')

Answer 1

 select task_id, user_id, count(user_id) as "count" from (
   select task_id, user_id from (
     select * from (
        select * from tasks order by tasks.created_at desc
     ) last_tasks group by project_id
   ) tasks_by_users INNER JOIN users ON tasks.task_id = tasks_users.task_id
 ) workload group by task_id, user_id;