Fix serialized data broken due to editing MySQL da

Question

Background: I downloaded a *.sql backup of my WordPress site's database, and replaced all instances of the old database table prefix with a new one (e.g. from the default wp_ to something like asdfghjkl_).

I've just learnt that WordPress uses serialized PHP strings in the database, and what I did will have messed with the integrity of the serialized string lengths.

The thing is, I deleted the backup file just before I learnt about this (as my website was still functioning fine), and installed a number of plugins since. So, there's no way I can revert back, and I therefore would like to know two things:

1. How can I fix this, if at all possible?

2. What kind of problems could this cause?

(This article states that, a WordPress blog for instance, could lose its settings and widgets. But this doesn't seem to have happened to me as all the settings for my blog are still intact. But I have no clue as to what could be broken on the inside, or what issues it'd pose in the future. Hence this question.)

Answer 1

This script (https://interconnectit.com/products/search-and-replace-for-wordpress-databases/) can help to update an sql database with proper URLs everywhere, without encountering serialized data issues, because it will update the "characters count" that could throw your URLs out of sync whenever serialized data occurs.

The steps would be:

1. if you already have imported a messed up database (widgets not working, theme options not there, etc), just drop that database using PhpMyAdmin. That is, remove everything on it. Then export and have at hand an un-edited dump of the old database.

2. Now you have to import the (un-edited) old database into the newly created one. You can do this via an import, or copying over the db from PhpMyAdmin. Notice that so far, we haven't done any search and replace yet; we just have an old database content and structure into a new database with its own user and password. Your site will be probably unaccessible at this point.

3. Make sure you have your WordPress files freshly uploaded to the proper folder on the server, and edit your wp-config.php to make it connect with the new database.
4. Upload the script into a "secret" folder - just for security reasons - at the same level than wp-admin, wp-content, and wp-includes. Do not forget to remove it all once the search and replace have taken place, because you risk to offer your DB details open to the whole internet.
5. Now point your browser to the secret folder, and use the script's fine interface. It is very self-explanatory. Once used, we proceed to completely remove it from the server.

This should have your database properly updated, without any serialized data issues around: the new URL will be set everywhere, and serialized data characters counts will be accordingly updated.

Widgets will be passed over, and theme settings as well - two of the typical places that use serialized data in WordPress.

Done and tested solution!