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SQL | More exotic joins exercise | Create self-joins between 3 levels of family hierarchies
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.
The answer to the exercise will be included and explained if you attend the course 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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First open the SQL file in the above folder in Management Studio, and execute it. This should generate a table called tblFamily.
Don't forget that you may need to refresh your tables to see this.
Each row in this table contains a column called ParentFamilyId, which tells you which parent family any family belongs to (the All categories family - number 25 - has no parent, and so sits at the top of the hierarchy).
Create a query which links 3 tables using outer joins as follows:
Add calculated columns to your query so that it displays all 25 familes:
If you display the families in FamilyName order, you should see something like this.
You'll need to trap for nulls, for those occasions when a family doesn't have a parent.
Save this query as Happy families, then close it down.
I'm having trouble getting this exercise done.
Is there anywhere i can get the solution?
Hello there, this one is kind of funky but here is my solution.
ISNULL('All categories' + ' > ' +
IIF(ParentFamily.FamilyId = 25,'',ParentFamily.[FamilyName]) + ' > ' +
TopFamily.[FamilyName], 'All categories') AS 'Family path'
[dbo].[tblFamily] AS Family
LEFT JOIN [dbo].[tblFamily] AS ParentFamily
ON Family.ParentFamilyId = ParentFamily.FamilyID
LEFT JOIN [dbo].[tblFamily] AS TopFamily
ON Family.FamilyId = TopFamily.FamilyID
I came up with this solution:
isnull(case when b.FamilyName = 'All categories' then '' else 'All categories < 'end +b.FamilyName +' < '+ a.FamilyName, 'All categories') as 'Family path'
left join tblFamily b on a.ParentFamilyId = b.FamilyID
Order by a.FamilyName