"Any ideas on how many people/sites use postgresql vs. mysql?"
No clue.
"Think postgresql will supplant mysql as the default installed database?"
Probably not. People prefer to have a small, fast database that let's them mess around with SQL wihtout having to worry abour consistency etc, rather than a complex-looking database that requires them to actually think about what they are doing 🙂
"Is postgresql significantly more difficult to install, admin, use, and/or etc.?"
Nope.
The installations of MYSQL and PostgreSQL are very similar, nothing fancy to either of them.
To use, PostgreSQL is a little more strict about SQL. MySQL lets you do things that are simply not possible in the real world, like selecting items in a group query without grouping on those elements. PostgreSQL will not do that.
In fact, PostgreSQL makes your life as a developer much easier, because you can enforce data consistency through foreign-key constraints and cascading deletes.
In MySQL you spend a lot of time making sure that you always delete all records that are linked to eachother, so you never get any orphan records. In postgreSQL, the database can make sure that you never get orphans. You can set it up so that if you erase the parent record, all it's related records are deleted automatically.
A forum, a FAQ, what else do you need?
