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Software ==> | SQL (203 exercises) |
Topic ==> | Basic joins (12 exercises) |
Level ==> | Harder than average |
Subject ==> | SQL training |
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.
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:
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 find other training resources for the subject of this exercise here:
From: | Bhavya59 |
When: | 01 Aug 24 at 08:27 |
SELECT [Title]
,AuthorName
,DoctorName
,EnemyName
,LEN(Title)+ LEN(AuthorName) + LEN(DoctorName) + LEN(EnemyName) AS TotalLength
FROM tblEpisode ep, tblAuthor a, tblDoctor d, tblEnemy en, tblEpisodeEnemy ee
WHERE
ep.AuthorId=a.AuthorId
AND ep.DoctorId=d.DoctorId
AND ep.EpisodeId=ee.EpisodeId
AND ee.EnemyId=en.EnemyId
AND (LEN(Title)+ LEN(AuthorName) + LEN(DoctorName) + LEN(EnemyName))<40
From: | sipi41 |
When: | 15 May 22 at 21:43 |
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 |
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 |
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
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