Question

I’m trying to create SQL Query to show task under one project and how many hours spent on each task month by month ?

Query

SELECT 
  Projects.projectName, Tasks.taskName, 
  billingsTimes.taskID, billingsTimes.actualTotalTime
FROM Projects 
INNER JOIN Projects_tasks ON Projects.projectID = Projects_tasks.projectID 
INNER JOIN Tasks ON Projects_tasks.taskID = Tasks.taskID 
INNER JOIN billingsTimes ON Tasks.taskID = billingsTimes.taskID
WHERE (Projects.projectID = '') 

Answer 1

Sounds like you just need the following:

select p.projectname,
    t.taskname,
    bt.taskid,
    bt.TotalTime
from projects p
left join projects_tasks pt
    on p.projectid = pt.projectid
left join tasks t
    on pt.taskid = t.taskid
left join
(
    select SUM(bt.actualTotalTime) TotalTime, bt.taskid
    from billingtimes bt
    group by bt.taskid
) bt
    on t.taskid = bt.taskid

If you provide more details about where the monthly dates are stored, then this could be altered to group by month to give you monthly totals per task.

edit #1, if you are using the dateOfService to determine when the service was performed and you want to group by month/year, then you can use the following:

select p.projectname,
    t.taskname,
    bt.taskid,
    bt.TotalTime,
    bt.ServiceMonth,
    bt.ServiceYear
from projects p
left join projects_tasks pt
    on p.projectid = pt.projectid
left join tasks t
    on pt.taskid = t.taskid
left join
(
    select SUM(bt.actualTotalTime) TotalTime, bt.taskid, 
        datepart(month, bt.dateofService) ServiceMonth,
        datepart(year, bt.dateofService) ServiceYear
    from billingtimes bt
    group by bt.taskid, datepart(month, bt.dateofService), 
        datepart(year, bt.dateofService)
) bt
    on t.taskid = bt.taskid