WISE OWL EXERCISES
- Simple Queries (4)
- Setting criteria using WHERE (5)
- Calculations (7)
- Calculations using dates (4)
- Basic joins (8)
- More exotic joins (2)
- Aggregation and grouping (8)
- Views (5)
- Subqueries (5)
- Stored procedures (5)
- Variables (8)
- Parameters and return values (11)
- Testing conditions (1)
- Looping (3)
- Scalar functions (6)
- Transactions (5)
- Creating tables (5)
- Temporary tables and table variables (9)
- Table-valued functions (6)
- Derived tables and CTEs (13)
- Dynamic SQL (4)
- Pivots (2)
- Triggers (2)
- Archived (70)
SQL | Aggregation and grouping exercise | Show which doctor/author combos are the most popular
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You can learn how to do this exercise if you attend the course listed below!
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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:
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:
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.
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