Solved

How to delete orphan records via foreign key not matched in another table

Posted on 2008-10-17
5
1,486 Views
Last Modified: 2008-10-22
I've been cleaning up my main table and have deleted lots of records.

I've now realised that I have orphan records in another table.

This is my select query which identifies the orphaned records..

SELECT Authors.AuthorID, Authors.FirstName
FROM Authors LEFT JOIN Pads ON Authors.AuthorID = Pads.AuthorID
WHERE (((Pads.AuthorID) Is Null));

I thought this would work...

Delete FROM Authors LEFT JOIN Pads ON Authors.AuthorID = Pads.AuthorID

But I get this error.

#1064 - You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'LEFT JOIN Pads ON Authors.AuthorID = Pads.AuthorID
WHERE (((Pads.AuthorID) Is N' at line 1

Can you provide me with a delete query which will do this or a solution to solve the problem.
WHERE (((Pads.AuthorID) Is Null));
0
Comment
Question by:mindwarpltd
  • 2
  • 2
5 Comments
 
LVL 17

Expert Comment

by:xDJR1875
ID: 22742435
I believe the real reason is that you want to isolate the delete to just the one table (Authors). So what you will want to do is use a subquery in the WHERE clause similar to the following.

FIRST, Are you trying to delete from the authors table or from the PADS table?

DELETE FROM AUTHORS
WHERE Authors.AuthorID = (SELECT Pads.AuthorID From PADS Where PADS.AuthorID Is Null)
...which could actually become
DELETE FROM AUTHORS WHERE Authors.AuthorID Is Null

if you want to delete from PADS
DELETE FROM PADS Where PADS.AuthorID Is Null

hope that gets you going.

Dan


0
 

Author Comment

by:mindwarpltd
ID: 22742480
I want to delete from the authors table.

I converted your first delete query into a select query, for safety.

SELECT *
FROM AUTHORS
WHERE Authors.AuthorID = (
SELECT Pads.AuthorID
FROM PADS
WHERE PADS.AuthorID IS NULL )
LIMIT 0 , 30

And it returned no records.

DELETE FROM AUTHORS WHERE Authors.AuthorID Is Null

This won't work as it has to relate to the pads table.
0
 
LVL 17

Expert Comment

by:xDJR1875
ID: 22742531
ok, try this last one

SELECT *
FROM AUTHORS
WHERE Authors.AuthorID = (
SELECT Authors.AuthorID
FROM Authors LEFT JOIN Pads ON Authors.AuthorID = Pads.AuthorID
WHERE (((Pads.AuthorID) Is Null))
)
0
 

Accepted Solution

by:
mindwarpltd earned 0 total points
ID: 22742579
I can do a select query, its the delete query I have problems with.

I figured out a solution.

Update Authors LEFT JOIN Pads ON Authors.AuthorID = Pads.AuthorID
Set Maint = 'D'
WHERE (((Pads.AuthorID) Is Null));

DELETE FROM `Authors` WHERE Maint = 'D';
0
 
LVL 6

Expert Comment

by:carlsiy
ID: 22742878
why not do this?

delete from
authors
where authors.authorID
in
(SELECT Authors.AuthorID
FROM Authors LEFT JOIN Pads ON Authors.AuthorID = Pads.AuthorID
WHERE (((Pads.AuthorID) Is Null)))
0

Featured Post

Backup Your Microsoft Windows Server®

Backup all your Microsoft Windows Server – on-premises, in remote locations, in private and hybrid clouds. Your entire Windows Server will be backed up in one easy step with patented, block-level disk imaging. We achieve RTOs (recovery time objectives) as low as 15 seconds.

Join & Write a Comment

Suggested Solutions

This guide whil teach how to setup live replication (database mirroring) on 2 servers for backup or other purposes. In our example situation we have this network schema (see atachment). We need to replicate EVERY executed SQL query on server 1 to…
Load balancing is the method of dividing the total amount of work performed by one computer between two or more computers. Its aim is to get more work done in the same amount of time, ensuring that all the users get served faster.
In this seventh video of the Xpdf series, we discuss and demonstrate the PDFfonts utility, which lists all the fonts used in a PDF file. It does this via a command line interface, making it suitable for use in programs, scripts, batch files — any pl…
Illustrator's Shape Builder tool will let you combine shapes visually and interactively. This video shows the Mac version, but the tool works the same way in Windows. To follow along with this video, you can draw your own shapes or download the file…

744 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question

Need Help in Real-Time?

Connect with top rated Experts

11 Experts available now in Live!

Get 1:1 Help Now