I run a number of web apps here in the house -- a copy of the macosxhints.com site, for instance, where I can experiment with changes before making them on the live site. I recently got rid of the machine I was using to host these sites, and migrated everything over to the Mac Pro. As part of that process, I had to install MySQL, which is basically a very simple operation. Just download the proper package from their downloads page, and run the installer.

When I did this, though, I didn't notice that the default download is MySQL version 5; for compatibility reasons, I actually wanted MySQL 4.1. Unfortunately, I got all the way through the install before I noticed that I had installed version 5. So I removed the MySQL 5 files in /usr/local, downloaded the 4.1 version, and ran its installer. Unfortunately, the installer told me I couldn't install 4.1, as I already had a newer version of MySQL on the machine -- even though I'd just deleted it.

After a bit of digging, I found the cause and the solution. The MySQL installer checks for the existence of other MySQL versions by looking in the /Library/Receipts folder, not by looking for an actual installed version of MySQL. So I deleted the MySQL receipts folder I found in /Library/Receipts (it was named something like mysql-standard-5.0.67-apple-darwin8.5.1-i686.pkg), then ran the 4.1 installer again. This time, MySQL installed without any problems, and my locally-hosted sites are up and running again.