I found this out the hard way – in moving a blog to another site, I dumped the SQL data for the blog, and then entered it into the new site (it’s a quick and dirty way of transferring a blog).

However, I thought I’d be creative, and change the database prefix from the default ‘wp_‘ to something more related to the blog.

That’s because I planned to combine multiple blogs on a single site, and wanted them to share a database (easier for backups).

However, once the tables are created, it’s VERY tricky to change the names.

For example, I thought I’d just go through and search and replace the SQL text

INTO `wp_

with

INTO `new_

and then

TABLE `wp_

with

TABLE `new_

However, these aren’t the only places where ‘wp_‘ occurs – and missing one of them (the user privileges) resulted in this error when I tried to log in:

“You do not have sufficient permissions to access this page.”

Now I know this is a common problem with WordPress MU – however, I had it with plain old vanilla WP (version 2.3.3 no less).

It didn’t help that I was doing several blogs at a time, and soon forget I had modified this database only – but when it became the only blog that wasn’t transferring properly, I became suspicious.

The moral? Tweak at your own risk – but be prepared to roll back if there’s a problem.

Another moral – change the WP extension in the wp-config.php file when you CREATE a new blog:

$table_prefix  = 'new_';

‘wp_‘ will end up clashing sooner or later, and it’s convenient to pack multiple blogs into the same database (and a bit faster, I suspect). If they’re all wp_user, wp_posts, etc, then you can’t combine them later.

And as a side benefit, you can backup your blog’s database at one time – and you can easily find the blog tables if you choose the prefix carefully.