SQL | Derived tables and CTEs exercise | Solve a complex question using CTEs and/or subqueries

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Software ==> SQL  (198 exercises)
Version ==> Any version of SQL Server
Topic ==> Derived tables and CTEs  (13 exercises)
Level ==> Harder than average
Courses ==> Introduction to SQL  /  Advanced SQL
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First run the script shown above to generate the Doctor Who training database.

Create a query which lists the David Tennant episodes for which none of the enemies appear in any non-David Tennant episodes:

Episode list

The first few of the 31 David Tennant episodes which don't share any enemies with any other non-Tennant episodes.

 

There are probably hundreds of ways to do this in SQL, and the answer given doesn't claim to use a particularly efficient one.

Optionally, save this query as Tennant only, then close it down. 

You can unzip this file to see the answers to this exercise, although please remember this is for your personal use only.
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svjmandryk   Reply to svjmandrykReply
01 Aug 20 at 17:04

Spoiler alert :)

********************************

my solution:

create function [dbo].[getAuthorId](@authorName varchar(max))

returns varchar(max)

as 

begin

    return 

        (select DoctorId 

            from tblDoctor 

            where lower(DoctorName) like '%' + @authorName)

end

 

go

 

create function [dbo].[getEpisodesByAuthor](@authorName varchar(max))

returns table

as 

    return select e.EpisodeId, e.Title, e.DoctorId, ee.EnemyId, ee.EpisodeEnemyId

    from tblEpisode as e

    left join tblEpisodeEnemy as ee

        on e.EpisodeId = ee.EpisodeId

    where DoctorId = [dbo].getAuthorId(@authorName)

 

go

 

create function [dbo].[getEpisodesNotByAuthor](@authorName varchar(max))

returns table

as 

    return select e.EpisodeId, e.Title, e.DoctorId, ee.EnemyId, ee.EpisodeEnemyId

    from tblEpisode as e

    join tblEpisodeEnemy as ee

        on e.EpisodeId = ee.EpisodeId

    where DoctorId <> [dbo].getAuthorId(@authorName)

        

go


 

create function [dbo].[getIdsOfEpisodeWithoutExclusiveEnemies](@authorName varchar(max))

returns table

as 

    return

        select distinct EpisodeId 

        from tblEpisodeEnemy

        where EnemyId in (

            select distinct EnemyId 

            from [dbo].[getEpisodesNotByAuthor](@authorName))

 

go

 

declare @authorName varchar(max) = 'Tennant'

 

select distinct EpisodeId, Title, DoctorId --, EnemyId, EpisodeEnemyId

from [dbo].[getEpisodesByAuthor](@authorName)

where 

    EpisodeId not in (

        select EpisodeId 

        from [dbo].getIdsOfEpisodeWithoutExclusiveEnemies(@authorName)) 

order by Title



ps - this was the trickiest one for me :)

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