WISE OWL EXERCISES
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- Derived tables and CTEs (11)
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SQL | Table-valued functions exercise | Create a function to list episodes for a given series and author
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First (if you haven't already done so) run the script shown above to generate the Doctor Who training database.
Create a function to list out the episodes for any given series number and part of an author name. This could begin:
CREATE FUNCTION fnChosenEpisodes(
For example, you could run this SQL query:
SELECT * FROM dbo.fnChosenEpisodes(1,'russell')
This would show the 9 series one episodes written by Russell T. Davies:
The first 2 or 3 of the 9 episodes in series 1 written by Russell T. Davies
Functions can't have optional parameters, but you can pass dummy values and detect them. Amend your function so that it shows:
- Episodes for any series if you pass the first argument as Null;
- Episodes for any author if you pass the second argument as Null.
To help you know whether you've succeeded, here's what 4 possible combinations should show:
-- there is 1 episode written by Steven Moffat for series 2
SELECT COUNT(*) FROM dbo.fnChosenEpisodes(2,'moffat')
-- -- there are 14 episodes in series 2 (for any author)
SELECT COUNT(*) FROM dbo.fnChosenEpisodes(2,null)
-- there are 32 episodes written by Steven Moffat (for any series)
SELECT COUNT(*) FROM dbo.fnChosenEpisodes(null,'moffat')
-- there are 117 episodes (any series, any author)
SELECT COUNT(*) FROM dbo.fnChosenEpisodes(null,null)
Optionally, save your query as Series and author.sql, then close it down.