Exercise: Create self-joins between 3 levels of family hierarchies

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Category ==> SQL  (192 exercises)
Topic ==> More exotic joins  (2 exercises)
Level ==> Harder than average
Course ==> Introduction to SQL
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.

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:

Table Alias
tblFamily Family
tblFamily ParentFamily
tblFamily TopFamily

Add calculated columns to your query so that it displays all 25 familes:

Families listed

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.

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