How to combine those three SQL queries - sql

Question

How to combine this three queries without giving me the same output ?
The first query is :
select
vwemployee.directorateName,
count(vwemployeeCourse.employeeId) as t1
from
vwemployee, vwemployeeCourse
where
vwemployee.directorateName = vwemployeeCourse.directorateName
group by
vwemployee.directorateName
This is the second query :
select
vwemployee.directorateName,
count(vwemployee.directorateName) as t2
from
vwemployee, employeeCourse
where
vwemployee.Id = employeeCourse.employeeId
group by
vwemployee.directorateName
This is the third query :
select
vwemployeeCourse.directorateName, sum(vwCourse.cost) as t3
from
vwemployeeCourse, vwCourse
where
vwemployeeCourse.courseId = vwCourse.Id
group by
vwemployeeCourse.directorateName
I will be using the combined query to generate a report
the t1 column should display how many courses this specific directorate took
the t2 column should display how many employee's under this directorate took this courses
the t3 column should display how much the courses cost for every directorate
So the total columns of the table of the combined query should be 4 columns
FYI: some nice people here helped me to combine the first two queries but it was not sample at all and i didn't succeed to add the third query to them since I am a beginner so please help me with a full simple query to understand it for future references

Answer 1

I think you are looking for something like this. We can achieve this using NESTED CTEs. You can see here I have created 3 nested CTEs, and in the end I have used all the three CTEs to get your result.
with cte1 as
(
select vwemployee.directorateName , count(vwemployeeCourse.employeeId) as t1
from vwemployee , vwemployeeCourse
where vwemployee.directorateName = vwemployeeCourse.directorateName
GROUP BY vwemployee.directorateName
)
,cte2 as
(
select vwemployee.directorateName , count(vwemployee.directorateName) as t2
from vwemployee , employeeCourse
where vwemployee.Id = employeeCourse.employeeId
GROUP BY vwemployee.directorateName
)
,cte3 as
(
select vwemployeeCourse.directorateName , sum(vwCourse.cost) as t3
from vwemployeeCourse , vwCourse
where vwemployeeCourse.courseId = vwCourse.Id
group by vwemployeeCourse.directorateName
)
select cte1.directorateName, cte1.t1, cte2.t2, cte3.t3
from
cte1 inner join cte2
on cte1.directorateName = cte2.directorateName
inner join cte3 on
cte2.directorateName = cte3.directorateName

Answer 2

First, you should be using explicit JOIN syntax. Simple rule: Never use commas in the FROM clause.
Then, given the three queries as written, with no other information, I think I would go for full outer join or union all with aggregation:
with ec as (
select e.directorateName, count(ec.employeeId) as t1
from vwemployee e join
vwemployeeCourse ec
on e.directorateName = ec.directorateName
group by e.directorateName
),
ed as (
select e.directorateName, count(ec.directorateName) as t2
from vwemployee e join
vwemployeeCourse ec
on e.id = ec. employeeId
group by e.directorateName
),
cc as (
select ec.directorateName, sum(c.cost) as t3
from vwemployeeCourse ec join
vwCourse c
ec.courseId = c.Id
group by ec.directorateName
)
select directoratename,
coalesce(t1, 0) as t1,
coalesce(t2, 0) as t2,
coalesce(t3, 0) as t3
from ((select directoratename, t1, null as t2, null as t3 from ec)
union all
(select directoratename, null as t1, t2, null as t3 from ed)
union all
(select directoratename, null as t1, null as t2, t3 from cc)
) t;
Having said that, I don't think this query can actually do anything useful. Joining two tables on two different keys, and then aggregating by the same key (as for ec and ed) is not usually done. If this doesn't produce the results you want, then ask another question, provide sample data, desired results, and a SQL Fiddle.