SQL | Parameters and return values exercise | Create a procedure setting null values for parameters

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Software ==> SQL  (198 exercises)
Version ==> Any version of SQL Server
Topic ==> Parameters and return values  (11 exercises)
Level ==> Average difficulty
Subject ==> SQL training
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.

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Create a stored procedure to list out the category name, event date and category id for each event:

Stored Procedures NULLS

Order your data by the event date.

Incorporate parameters for the following:

Parameter Should equal
@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.

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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