Question

I have some networked equipment that’s attached to multiple networks/VLans (A, B & C), and other equipment that’s just connected to one of the networks. When I remove or replace a network, I need to update my database to reflect what the equipment is attached to so I’m trying to write a mysql statement to do that, but I’m running into various road blocks.

My table only has two fields and there cannot be duplicate records. My data example is

deviceID network
1        A
1        B
1        C
2        B
2        C
3        A
4        A
5        B

How can I merge network A into network B so the above table would look like…

deviceID network
1        B
1        C
2        B
2        C
3        B
4        B
5        B

My initial attempt was to just set network = 'B' where network = 'A', followed by a DELETE network 'A' statement but that would create duplicates, which isn’t allowed for that table – even though the duplicates would be brief. Using alternate methods, I just keep running into failed mysql statements by using WHERE EXISTS and various FROM (SELECT) statements. Is it possible to do in a single mysql statement? Do I need two?

Any help is appreciated.

Answer 1

You could use UPDATE IGNORE with your update statement – this would skip any updates that caused duplicates. You would then follow this with a DELETE to clear the rows that had been skipped. For example:

UPDATE IGNORE mytable SET network = 'B' WHERE network = 'A';
DELETE FROM mytable WHERE network = 'A';

From the documentation:

With the IGNORE keyword, the update statement does not abort even if
errors occur during the update. Rows for which duplicate-key conflicts
occur are not updated. Rows for which columns are updated to values
that would cause data conversion errors are updated to the closest
valid values instead.