SQL | Aggregation and grouping exercise | Show which doctor/author combos are the most popular

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.

You can learn how to do this exercise if you attend one of more of the courses listed below!

Software ==> SQL  (198 exercises)
Version ==> Any version of SQL Server
Topic ==> Aggregation and grouping  (8 exercises)
Level ==> Average difficulty
Classroom ==> Introduction to SQL  /  Fast-track SQL
Online ==> Introduction to SQL  /  Fast-track SQL
Before you can do this exercise, you'll need to download and unzip this file (if you have any problems doing this, click here for help).

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

The tables you'll need for this exercise are as follows:

Three tables needed

You'll need to link each episode to its author and its doctor.

Write a query to list out for each author and doctor the number of episodes made, but restrict your output to show only the author/doctor combinations for which more than 5 episodes have been written.  Here's what you should see:

Episode listing

Here we've sorted the rows so the most common combination appears first.

 

You'll need to use the HAVING clause.  Remember that sweaty feet will give horrible odours!

Save this as Favourite combos, 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.
This page has 2 threads Add post
walteragwe   Reply to walteragweReply
21 Jan 21 at 03:09

SELECT [AuthorName],[DoctorName],COUNT([EpisodeId]) AS [No of episodes]
FROM   [dbo].[tblAuthor]  A INNER JOIN [dbo].[tblEpisode] E
ON   A.AuthorId = E.AuthorId INNER JOIN [dbo].[tblDoctor] D
ON   E.DoctorId = D.DoctorId
GROUP BY [AuthorName],[DoctorName]
HAVING COUNT([EpisodeId]) > 5
ORDER BY [No of episodes] DESC;
GO

smyndlo   Reply to smyndloReply
24 Nov 19 at 13:54

SELECT  
        au.AuthorName Writer, --1st Table
        Doc.DoctorName Doctor, --2nd Table
        COUNT(Ep.EpisodeId) 'Num Of Episodes' --3rd Table
FROM tblAuthor AS Au
    INNER JOIN tblEpisode AS Ep
    ON Au.AuthorId = Ep.AuthorId
    INNER JOIN tblDoctor Doc
    ON Doc.DoctorId = Ep.DoctorId
GROUP BY Au.AuthorName, Doc.DoctorName
HAVING COUNT(Ep.EpisodeId) > 5
ORDER BY [Num Of Episodes] Desc

Andy B   Reply to Andy BReply
25 Nov 19 at 09:33

We don't normally post answers to exercises, as it removes the incentive for people to try them, but I've made an exception for this because the query is so well-written and presented!

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