SQL | Triggers exercise | Create a trigger to stop people deleting UK events

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You can learn how to do this exercise if you attend one of more of the courses listed below!

Software ==> SQL  (198 exercises)
Version ==> Any version of SQL Server
Topic ==> Triggers  (2 exercises)
Level ==> Harder than average
Classroom ==> Fast-track SQL  /  Advanced SQL
Online ==> Fast-track 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 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.

You can unzip this file to see the answers to this exercise, although please remember this is for your personal use only.
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