Exercise: Create a trigger to stop people deleting UK events

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.

The answer to the exercise will be included and explained if you attend the course listed below!

Category ==> SQL  (192 exercises)
Topic ==> Triggers  (2 exercises)
Level ==> Harder than average
Course ==> 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).

You need a minimum screen resolution of about 700 pixels width to see our exercises. This is because they contain diagrams and tables which would not be viewable easily on a mobile phone or small laptop. Please use a larger tablet, notebook or desktop computer, or change your screen resolution settings.

The aim of this exercise it to stop anyone deleting events which happened in the UK (country number 7).  To do this create a trigger which operates on the tblEvent table.

Use INSTEAD OF UPDATE rather than AFTER UPDATE, so that the deletion won't occur unless you specifically authorise it.

In your trigger, create and set the value of the following two variables from the deleted table:

Variable What it should contain
@EventId The number of the event someone is trying to delete
@CountryId The country number in which this event took place.

If this event didn't take place in country id number 7, delete it:

-- if country is not UK (7), allow deletion

IF @CountryId <> 7

BEGIN

DELETE

FROM tblEvent

WHERE EventId = @EventId

END

Test that your query works by deleting events which did and didn't happen in the UK.

Be careful!  When doing this manually by editing rows, the number of rows reported can be wrong.  You may need to close your table and then re-open it to check that UK events haven't been deleted.

Optionally, save this query as Brexit events.sql, then close it down.

This page has 0 threads Add post