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Software ==>	SQL (203 exercises)
Topic ==>	Calculations (18 exercises)
Level ==>	Average difficulty
Subject ==>	SQL training

Use IsNull, Coalesce and/or CASE WHEN to replace nulls with values

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.

Before you can do this exercise, you'll need to download and unzip this file . Once you've done this:

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).

The tblContinent table lists out the world's continents, but there are gaps:

You need to fill in the gaps! Read on ...

Add up to 3 columns to show a message where a summary is missing:

This is what your query should show - see notes below.

Here's what your 3 columns should use:

Column	How to get it
Using ISNULL	Use the IsNull function to substitute the words No summary for rows where the Summary column is null.
Using COALESCE	Do the same thing, but using the COALESCE function instead.
Using CASE	Use a CASE WHEN statement to show different things according to whether the Summary column is null or not.

Take a moment to think which method you liked best, then save your query as Missing summaries 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.

You can find other training resources for the subject of this exercise here:

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From:	Bhavya59
When:	31 Jul 24 at 11:07

SELECT TOP (1000) [ContinentID]

,[ContinentName]

,[Summary]

--USING ISNULL

,ISNULL(Summary,'No Summary') AS UsingISNULL

--USING CASE

,CASE

WHEN Summary IS NULL THEN 'No Summary'

ELSE Summary

END

AS UsingCASE

--Using COALESCE

,COALESCE (Summary,'No Summary') AS UsingCOALESCE

FROM [WorldEvents].[dbo].[tblContinent]

From:	Yash2211
When:	13 Sep 23 at 17:46

select *,isnull(summary,'No summary') as 'Using isnull',coalesce(summary,'No summary') as 'Using Coalensce',
case
when summary is null then 'No Summary' else Summary
end 'Using case'

from tblContinent

From:	Chinmaykumar
When:	28 Jun 23 at 11:58

Query_Sol. for MySQL users

-- In MySQL, ISNULL() just returns null values with 0,1
-- To replace values of null I used IFNULL(expression, alt_value)

SELECT ContinentName, Summary,
IFNULL(Summary,'No summary') AS 'Using ISNULL',
COALESCE(Summary,'No summary') AS 'Using COALESCE',
CASE
WHEN Summary IS NULL THEN 'No summary'
ELSE Summary
END AS 'Using CASE'
FROM tblcontinent;

From:	SaratSQLnoob
When:	05 Feb 22 at 10:53

My Solution:

Alter Table tblContinent
Add [Using ISNUll] nvarchar(50) NULL

Alter Table tblContinent
Add [Using COALESCE] nvarchar(50) NULL

Alter Table tblContinent
Add [Using CASE] nvarchar(50) NULL

Update dbo.tblContinent
Set [Using ISNULL] = ISNULL(Summary, 'No Summary')

Update dbo.tblContinent
Set [Using COALESCE] = COALESCE(Summary, 'No Summary')

Update dbo.tblContinent
Set [Using CASE] = CASE WHEN Summary is NOT NULL Then Summary Else 'No Summary' END

From:	Vidhi
When:	18 Jul 18 at 21:55

select
Continentid, continentName, Summary,
ISNULL(Summary,'No Summary') as 'Using IsNull',
Coalesce(Summary,'No Summary') as 'Using COALESCE',
case
when summary is null then 'No Summary'
else summary
end
as 'Using Case'
from tblContinent

From:	BillyUhn
When:	04 Jun 17 at 17:33

The WorldEvents database table dbo.tblContinent that I downloaded doesn't have a third column. Is that the case for others?

From:	Andy B
When:	05 Jun 17 at 09:40

You're right! I've updated the download file, and it should now be fine. Thanks.

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EXERCISE TOPIC

SQL EXERCISES

SQL EXERCISES

Use IsNull, Coalesce and/or CASE WHEN to replace nulls with values

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