如何合并这三个SQL查询

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.