Exercise: Show the number of events for the top 3 categories/countries

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The answer to the exercise will be included and explained if you attend one of more of the courses listed below!

Category ==> SQL  (156 exercises)
Topic ==> Derived tables and CTEs  (8 exercises)
Level ==> Harder than average
Courses ==> Introduction to SQL  /  Advanced 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). Once you've done this:
  1. Go into SQL Server Management Studio;
  2. Open the SQL file you've just unzipped (you can press CTRL + O to do this); then
  3. Execute this script.

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Create two CTEs in the same query as follows:

CTE What it should list out
TopCountries The ids of the 3 countries with the most events (use TOP 3)
TopCategories The ids of the 3 categories with the most events (use TOP 3 again)

Use these to show all possible combinations in a final SELECT statement which should look like this:

-- combine these together (every possible combination)

SELECT

cy.CountryID,

cg.CategoryID

FROM

TopCountries AS cy

CROSS JOIN TopCategories AS cg

The cross join gives all possible combinations of rows in the two CTEs - see overleaf for what the results should look like.

You should now be looking at something like this:

Cross join results

There are 9 possible combinations.

 

If you still have the energy, use this to show the number of events for each combination:

Combination of events - full list

United Kingdom / Politics is the combination of country and category which has the most events.

 

Save this as Country category combinations, then close it down. 

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