Exercise: Create a CTE to make it easier to group by an expression

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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  (192 exercises)
Topic ==> Derived tables and CTEs  (11 exercises)
Level ==> Relatively easy
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.

This will generate the database that you'll need to use in order to do this exercise (note that the database and script are only to be used for exercises published on this website, and may not be reused or distributed in any form without the prior written permission of Wise Owl).

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The aim of this exercise is to show the number of events whose descriptions contain the words this and/or that:

This and that

Only 3 events have the holy grail: both THIS and THAT.

 

To do this you can find all events whose EventDetails column contains the word this or that respectively, using the LIKE keyword.

In a single query solution you would have to use a CASE expression to determine the value of IfThis and IfThat, then group by the same CASE expression.  This is messy, and makes it hard to make subsequent changes to your expression (as you have to do it in two places).  Read on!

Create a query to solve this problem in two passes:

Pass What to do
1 Create a CTE (called ThisAndThat?) to determine the values of the IfThis and IfThat flags for each event.
2 Use this CTE to get the required results, as shown at the start of this exercise.

As an aide-memoire, here is the syntax for a CTE:

-- create CTE

WITH CteName AS (

SELECT ...

)

-- then immediately use it

SELECT ... FROM CteName

If you get this working and still have spare time, try changing or extending your query to show the 3 events whose details contain both this and that:

This and that events

Other than the text they contain, there's no obvious link between these 3 events.

Optionally, save this query as This and that.sql, then close it down. 

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