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SQL | Triggers 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.
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 |
| Courses ==> | Fast-track SQL / Advanced SQL |
- Go into SQL Server Management Studio;
- Open the SQL file you've just unzipped (you can press CTRL + O to do this); then
- 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.