Avatar of Member_2_99151
Member_2_99151
 asked on

SQL Query to get orphaned nodes

Hi all,
I have an interesting query that I am trying to create...

I have a table that contains entities, each of these *may* have a parent (only single level)

What I would like to do is query the table to find entries that say they have a parent, but the parent entry does not exist.

tblData
ID, DESCRIPTION, PARENT
'A','Main Parent','-'
'B','First Child','A'
'C','Second Child','A'
'D','Another Parent','-'
'E','An Orphan','Z'

In this example, I would like to execute a query to get the record relating to 'E'

I've tried a few ways, but can't get it to work!!!

Any ideas would be very much appreciated..

Thanks a lot,

James
Microsoft SQL ServerDatabases

Avatar of undefined
Last Comment
Member_2_99151

8/22/2022 - Mon
ASKER CERTIFIED SOLUTION
Snarf0001

Log in or sign up to see answer
Become an EE member today7-DAY FREE TRIAL
Members can start a 7-Day Free trial then enjoy unlimited access to the platform
Sign up - Free for 7 days
or
Learn why we charge membership fees
We get it - no one likes a content blocker. Take one extra minute and find out why we block content.
Not exactly the question you had in mind?
Sign up for an EE membership and get your own personalized solution. With an EE membership, you can ask unlimited troubleshooting, research, or opinion questions.
ask a question
SOLUTION
Phillip Burton

Log in or sign up to see answer
Become an EE member today7-DAY FREE TRIAL
Members can start a 7-Day Free trial then enjoy unlimited access to the platform
Sign up - Free for 7 days
or
Learn why we charge membership fees
We get it - no one likes a content blocker. Take one extra minute and find out why we block content.
Not exactly the question you had in mind?
Sign up for an EE membership and get your own personalized solution. With an EE membership, you can ask unlimited troubleshooting, research, or opinion questions.
ask a question
ste5an

You should use a foreign key constraint to avoid this situation.

SELECT  C.*
FROM    #tblData C
        LEFT JOIN #tblData P ON C.PARENT = P.ID
WHERE   P.ID IS NULL;

Open in new window

Member_2_99151

ASKER
Perfect!!! Thanks :-)
Hope it is okay to split points equally as there was only 1 minute between posts!
Your help has saved me hundreds of hours of internet surfing.
fblack61