SQL Fairy, also known as SQL::Translator, is a tool for building SQL out of a database-neutral specification. Besides having a cute logo, it's one of the easiest ways to build your plugin's data description SQL for all SQL databases MT supports. (Future versions of MT will hopefully support 3.2's new automatic upgrading in all MT::Objects, so you'd only have to define the data types of your fields and let MT do the rest.) Byrne asked me to convert his MySQL schema for Media Manager to Postgres, so I thought I'd point out how easy it was with SQL::Translator.
First, download and install SQL::Translator. It's a standard Perl module with no binaries, so it's pretty easy. (If you install the libraries to a nonstandard directory because you aren't the superuser, remember to copy the scripts in the bin directory to somewhere in your path as well.)
Once it's installed, you should have an sqlt command you can run to do the translation. A typical command line might be:
sqlt -f MySQL -t PostgreSQL schemas/mysql.dump > schemas/postgresql.dump
This would translate the tables described in mysql.dump from MySQL's particular SQL syntax to that of PostgreSQL. That's fine if you have a favorite database, but if your SQL is rusty, you can specify your tables in a neutral format like YAML. Your SQL would have to be pretty rusty, though, because the YAML generated from SQL or a live database looks pretty complicated. (It's really just a serialization of the objects it parses the SQL into before translating to another kind of SQL.)
I was able to use the MT::Upgrade system for my OpenID Comments plugin, but it was a bit complicated and not documented at all, so I can't recommend that method until it's officially supported. If like most people you develop plugins on one particular database, you can use SQL::Translator to cover all the SQL databases Movable Type does.
