This page has 4 threads | Add post

Finding our exercises useful? Please consider helping us to share more!

Software ==>	SQL (129 exercises)
Topic ==>	More exotic joins (2 exercises)
Level ==>	Harder than average
Subject ==>	SQL training

Create 2 self-joins between a table of families and itself, to show families, their parents and their grandparents

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).

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:

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.

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:

This page has 4 threads

Add a new post

From:	FloridaMan
When:	26 Sep 21 at 13:43

Reply to FloridaMan

Not sure if I can post this, BUT I found a great video explaining this.

https://youtu.be/ck8mVDOOCCg

From:	ShukiMolk
When:	11 Apr 20 at 22:07

Reply to ShukiMolk

Here's my solution:

SELECT
   lv3.FamilyName,
   (ISNULL(lv1.FamilyName + ' -> ', '') + ISNULL(lv2.FamilyName + ' -> ' , '') + lv3.FamilyName)
   AS 'Family Path'
FROM
   tblFamily lv3
   LEFT JOIN tblFamily lv2
   ON lv3.ParentFamilyId = lv2.FamilyID
       LEFT JOIN tblFamily lv1
       ON lv2.ParentFamilyId = lv1.FamilyID
ORDER BY
lv1.familyid, lv2.familyid, lv3.familyid

But yeah, I also used LEFT JOIN instead of FULL OUTER JOIN

From:	hjay629
When:	20 Feb 19 at 06:12

Reply to hjay629

This question is tricky because there are many ways you can do it. In fact, you don't even have to use "null traps", nor all the aliases and joins mentioned in the problem. However, I am not 100% sure this is the way Wise Owl wanted it to be done nor am I sure this is correct. Proceed with caution!

ISNULL(Expression, 'All categories') Function

Checks if any of the arguments in the function is NULL, in this case whether if there is a family of a higher hierarchy, and returns the Top Hierarchy 'All categories'.

Note: The program reads the hierarchy from Lowest->Highest. If there are only two levels the TopFamily becomes NULL and if only one level the TopFamily and ParentFamily become NULL , so on. Family < Parent Family < Top Family [Lowest< Middle < Highest].

CASE

I used a CASE here to check if ONLY the TopFamily is NULL, if it's NULL it will return '' and if it's not NULL it will return the rest of the function if it exists. I did this so that the ISNULL() function does not make every row with less than 3 levels of hierarchy = 'All categories'.

The rest of the function is simple, a basic string calculation to add the remainder of the FamilyNames in the hierarchy.

LEFT JOIN

TopFamily being the highest in the hierarchy, I set it as ParentFamily's ParentFamilyID and Family's ParentFamilyID as ParentFamily's FamilyID. Thus, TopFamily.FamilyID = ParentFamily.ParentFamilyID and Family.ParentFamilyID = ParentFamily.FamilyID.

You can see this more clearly by executing the code below, where I wrote it so that it generates all the revelant FamilyIDs and ParentFamilyIDs

---SPOILER [ANSWER]---

SELECT
---FOR CLARITY---
TopFamily.FamilyID as [TopFamily FamilyID],
ParentFamily.ParentFamilyID as [ParentFamily ParentFamilyID],
ParentFamily.FamilyID as [ParentFamily FamilyID],
Family.ParentFamilyId as [Family ParentFamilyID],
Family.FamilyID as [Family FamilyID],
Family.FamilyName,

ISNULL(
       CASE
WHEN TopFamily.FamilyName IS NULL
THEN ''
ELSE TopFamily.FamilyName + ' > '
       END + ParentFamily.FamilyName + ' > ' + Family.FamilyName

       , 'All categories'


) as 'Family path'
FROM
tblFamily as family
LEFT JOIN
tblFamily as ParentFamily
ON ParentFamily.FamilyID = Family.ParentFamilyID
LEFT JOIN
tblFamily as TopFamily
ON TopFamily.FamilyId = ParentFamily.ParentFamilyID
ORDER BY

FamilyName

From:	odkao
When:	29 Jun 18 at 14:17

Reply to odkao

Hello.

I'm having trouble getting this exercise done.

Is there anywhere i can get the solution?

From:	Phithel
When:	19 Oct 18 at 21:10

Reply to Phithel

Hello there, this one is kind of funky but here is my solution.

USE WorldEvents

SELECT
   Family.[FamilyName],
   ISNULL('All categories' + ' > ' +
   IIF(ParentFamily.FamilyId = 25,'',ParentFamily.[FamilyName]) + ' > ' +
   TopFamily.[FamilyName], 'All categories') AS 'Family path'
FROM
   [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
ORDER BY
   Family.[FamilyName]

From:	wagnnerfh
When:	01 Feb 20 at 14:25

Reply to wagnnerfh

Hi.

I solved this way following the instructions of Wise Owl (outer joins).

SELECT Family.FamilyName,
(TopFamily.FamilyName + ' > ' + ParentFamily.FamilyName + ' > ' + Family.FamilyName) AS FamilyPath

FROM tblFamily AS TopFamily

FULL OUTER JOIN tblFamily AS ParentFamily

ON TopFamily.FamilyID = ParentFamily.ParentFamilyId

FULL OUTER JOIN tblFamily AS Family

ON ParentFamily.FamilyID = Family.ParentFamilyId

WHERE Family.ParentFamilyId IS NOT NULL
   AND Family.FamilyName IS NOT NULL
   AND ParentFamily.ParentFamilyId IS NOT NULL
   AND ParentFamily.FamilyName IS NOT NULL
   AND TopFamily.FamilyName IS NOT NULL
   AND TopFamily.FamilyID IS NOT NULL

From:	SmartSqler
When:	13 Jul 18 at 13:30

Reply to SmartSqler

Hey,

I came up with this solution:

select
a.FamilyName,
isnull(case when b.FamilyName = 'All categories' then '' else 'All categories < 'end +b.FamilyName +' < '+ a.FamilyName, 'All categories') as 'Family path'

from
tblFamily a
left join tblFamily b on a.ParentFamilyId = b.FamilyID

Order by a.FamilyName

From:	SeahawkZim
When:	21 Mar 20 at 19:23

Reply to SeahawkZim

Perfectly elegant. Did you have to spend much time on the answer to this? Or, was it intuitive?

From:	Andy B
When:	29 Jun 18 at 18:43

Reply to Andy B

We don't publish the exercises, I'm afraid - but you never know, some kind person might help ....

Add a new post

Book any course as classroom, onsite or online training, or as one-to-one consultancy

Free resources

Paid services

Getting help

Where we are

Where you are

Online

Transparent reviews

Delivery of courses

Nicer to work with

Reliable and established

Our training courses

C#

Excel

Google Sheets

MySQL

Power Apps

Power Automate

Power BI and DAX

Python

Report Builder

SQL

SQL Server

VBA Macros

Other training resources

Blogs

Exercises

YouTube tutorials

YouTube shorts

Test your skills

Consultancy

Courseware

Self-paced courses

Newsletters

Publications

Our training venues

London

Manchester

Across the UK

At your site

Online

Why we are different

Hundreds of published reviews

Small class sizes

Outstanding courseware

Online classroom

(Almost) no cancellations

Wise Owl trainers only

Genuine integrity

Invoices after training

30+ years of Wise Owl

Our top 100 clients

EXERCISE TOPIC

SQL EXERCISES

SQL EXERCISES

Create 2 self-joins between a table of families and itself, to show families, their parents and their grandparents

Head office

London

Manchester