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SQL | Parameters and return values exercise | Create a procedure setting null values for parameters
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!
- 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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Create a stored procedure to list out the category name, event date and category id for each event:
Order your data by the event date.
Incorporate parameters for the following:
|@CategoryName||All or part of the name of the category you're looking for|
|@After||The earliest event date you're looking for|
|@CategoryId||The number of the category you're looking for|
Now try adding default values to the parameters and you'll see that it's difficult: what should the default be for @CategoryID? Instead assign NULL as the default value for all 3 parameters:
(@CategoryName varchar(100) = NULL
,@After DATETIME = NULL
,@CategoryID INT = NULL)
This in itself won't work, but NULL is a consistent value across all data types which we can test for. Add an OR to the WHERE clause which tests if each parameter is NULL. For example:
(@CategoryName IS NULL OR CategoryName LIKE '%' + @CategoryName + '%')
You could now test your stored procedure - here are some numbers it should return:
-- there should be 14 events since 1990 about death
EXEC uspCategoryEvents @CategoryName='death', @After='19900101'
-- category 16 is "Royalty", which has 16 events
EXEC uspCategoryEvents @CategoryId=16
Optionally save this as Dull as a NULL.sql and close it down.