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Software ==>	SQL (129 exercises)
Topic ==>	Basic joins (9 exercises)
Level ==>	Harder than average
Subject ==>	SQL training

Use inner joins to link lots of tables together, with a WHERE clause

This exercise is provided to allow potential course delegates to choose the correct Wise Owl Microsoft training course, and may not be reproduced in whole or in part in any format without the prior written consent of Wise Owl.

Before you can do this exercise, you'll need to download and unzip this file.

If you haven't already done so, run the script in the above folder to generate the Doctor Who database.

Create a query to list out the appearances of enemies in episodes which have length under 40 characters, where the length is defined as the sum of:

the number of characters in the author's name;
the number of characters in the episode's title;
the number of characters in the doctor's name; and
the number of characters in the enemy's name.

This should reveal two episodes:

The two episodes which make it under the very low bar.

You are now a master (or mistress) of joins! Save this as Time for a coffee, 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.

You can find other training resources for the subject of this exercise here:

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From:	sipi41
When:	15 May 22 at 21:43

Reply to sipi41

The proposed solution was to sum the columns at the select part, then do the same when doing the WHERE. I was thinking about other solutions, but after carefully considering my solution: (where I encapsulated the result of the joins, then used the WHERE to filter) I'm starting to think this could create a very bad performance problem because it basically return all rows from the joins.

select * from (
   select
       aut.AuthorName, e.Title, doc.DoctorName, enemy.EnemyName,
       (
           len(aut.AuthorName) +
           len(e.Title) +
           len(doc.DoctorName) +
           len(enemy.EnemyName)
       ) AS [Total Length]
   from
   tblAuthor aut
   inner join tblEpisode e
       on e.AuthorId = aut.AuthorId
   inner join tblDoctor doc
       on doc.DoctorId = e.DoctorId
   inner join tblEpisodeEnemy epen
       on E.EpisodeId = EPEN.EpisodeId
   INNER JOIN tblEnemy enemy
       on epen.EnemyId = enemy.EnemyId
) AS r
WHERE
   r.[Total Length] < 40

My question is... would you please say if my solution is bad, and what would be the advantage of calculating during selection then repeating the calculation on the where again... thank you for all your help!

From:	Andy B
When:	16 May 22 at 09:47

Reply to Andy B

To be honest I don't know! My gut feeling is that it would be better to do the calculation once only, as you've done. I'll throw this question open - anyone else out there know the answer?

From:	Aravindh_sql
When:	27 May 22 at 08:23

Reply to Aravindh_sql

SELECT tblAuthor.AuthorName,
tblEpisode.Title,
tblDoctor.DoctorName,
tblEnemy.EnemyName,
(LEN(tblAuthor.AuthorName)+

LEN(tblEpisode.Title)+
   LEN(tblDoctor.DoctorName)+
   LEN(tblEnemy.EnemyName)) AS [Total Length]

FROM tblEpisodeEnemy

INNER JOIN
tblEnemy ON tblEpisodeEnemy.EnemyId = tblEnemy.EnemyId

INNER JOIN
tblAuthor

INNER JOIN
tblEpisode ON tblAuthor.AuthorId = tblEpisode.AuthorId

INNER JOIN
tblDoctor ON tblEpisode.DoctorId = tblDoctor.DoctorId
ON tblEpisodeEnemy.EpisodeId = tblEpisode.EpisodeId

WHERE (LEN(tblAuthor.AuthorName)+LEN(tblEpisode.Title)+
LEN(tblDoctor.DoctorName)+
LEN(tblEnemy.EnemyName)) <40

First of all Use Query Editor to Create the joins among the tables tblDoctor, tblAuthor,tblEpisode, tblEnemy,tblEpisodeEnemy
And then use len function to write query

From:	hjay629
When:	19 Feb 19 at 21:43

Reply to hjay629

For Amy's choice my enemy name says 'Winifred GillyFlower'.

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SQL EXERCISES

Use inner joins to link lots of tables together, with a WHERE clause

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