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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.
|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 (
aut.AuthorName, e.Title, doc.DoctorName, enemy.EnemyName,
) AS [Total Length]
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
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!
|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?
|When:||27 May 22 at 08:23|
LEN(tblEnemy.EnemyName)) AS [Total Length]
tblEnemy ON tblEpisodeEnemy.EnemyId = tblEnemy.EnemyId
tblEpisode ON tblAuthor.AuthorId = tblEpisode.AuthorId
tblDoctor ON tblEpisode.DoctorId = tblDoctor.DoctorId
ON tblEpisodeEnemy.EpisodeId = tblEpisode.EpisodeId
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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