PHP - Mysql vs Mysqli vs open database conns

There is an ongoing question over what database the application should use,
and indeed whether it should be database independent.

My view on this is that there is pretty much only MySQL. It is free, fast,
scalable, widely used and easy to find support for. Beyond MySQL, there is
Oracle which isn't free, but is more scalable for certain types of
application. Importantly, if it is being used in a site with expertise in
some other database, MySQL really can be left alone, and it will work away
happily without needing maintenance.

Of course MySQL won't be free forever now that Sun own it, and upgrades are
likely to be sporadic with the best features being a cost option.

MySQL also has two distinct php interfaces. MySQLI, and the older MySQL. The
uptake of MySQLI has been relatively poor even though it has been out for a
few years, possibly because there isn't currently an implementation for a
persistent connection.

As a consequence of all this, there are a few design philosophies:

- All database connections are controlled through a single include.php, the
class needs to be extended in order to be used.
- All SQL outside the class needs to be ANSI-99.
- Accomodating a new database should only need a quick whip through the
parent class. An hour or so's work.
- I am using MySQLI as an interface, although it should be a simple matter
to revert to MySQL, or indeed implement memcache within the parent if
necessary.

...job done, and I am not giong to even bother with the complexities of user
configured database connections. In practise, the configuration of DB
connections gives rise to at least 50% of all installation problems anyway.