Inner Join Sql Query

Question

I have a question which has 3 tables:

1.Review(JobID)

2.Job(BusinessNumber)

3.Business(BusinessNumber) (Foreign Keys).

I need to retrieve data and create table which has 4 columns HighestBusiness , HighestRating , LowestBusiness , Lowest Rating .

select business.businessname AS HIGHESTRATEDBUSINESS, 
        max(review.reviewrating) as HIGHEST
from business 
    inner join job 
        on job.selectedbusinessabnnumber=business.abnnumber 
    inner join review 
        on review.jobid=job.jobid 
where review.reviewrating = (select max(reviewrating)
                             from review)  
GROUP BY businessname 
UNION 
select business.businessname AS LOWESTRATEDBUSINESS, 
     MIN(review.reviewrating) as HIGHEST
from business 
    inner join job 
        on job.selectedbusinessabnnumber=business.abnnumber 
    inner join review 
         on review.jobid=job.jobid 
where review.reviewrating = (select MIN(reviewrating)
                               from review)
GROUP BY businessname
/

I didn't create table as of now, I just wanted the four columns to be shown.

Answer 1

The UNION operator produces one result set from two sets with the same projection. What you need is a new projection of four columns. So turn the two sub-queries into inline views and use a CROSS JOIN:

select h.highestratedbusiness
       , h.highest
       , l.lowestratedbusiness
       , l.lowest
from
    (select business.businessname AS HIGHESTRATEDBUSINESS, 
            max(review.reviewrating) as HIGHEST
    from business 
        inner join job 
            on job.selectedbusinessabnnumber=business.abnnumber 
        inner join review 
            on review.jobid=job.jobid 
    where review.reviewrating = (select max(reviewrating)
                                from review)  
    GROUP BY businessname ) h
cross join 
        (select business.businessname AS LOWESTRATEDBUSINESS, 
             MIN(review.reviewrating) as HIGHEST
        from business 
            inner join job 
                on job.selectedbusinessabnnumber=business.abnnumber 
            inner join review 
                 on review.jobid=job.jobid 
        where review.reviewrating = (select MIN(reviewrating)
                                       from review)
        GROUP BY businessname ) l
/

A CROSS JOIN produces one record for each combination of records in the joined sets. This will be fine when the data produces one highest rated business and one lowest rated business. But it will generate a Cartesian product if there's a tie in either or both places. There are ways around that, so please refine your question if that is a roadblock for you.