One of the great selling points of PostgreSQL is its pluggable PL language architecture. MySQL is known for its pluggable storage and
PostgreSQL is known for its pluggable PL language architecture. From Monty's notes on slide 12 looks like MySQL
may be working on a pluggable PL language architecture of their own.
The most common of these languages are the all-purpose languages SQL and C (these are built-in and not really PLs like the others, but we'll throw them in there),
PLPgSQL which is also built-in but not always enabled, PL/Perl, PL/Python, and the domain specific languages PL/R, PL/SH and gaining popularity Skype released PL/Proxy.
There are others in the family such as PL/Tcl, PL/PHP, PL/Ruby, PL/Scheme (a dialect of Lisp), PL/Java, PL/Lua and PL/LOLCode (for kicks and as a reference implementation. Think of LOLCode as PostgreSQL Pluggable PL equivalent of MySQL's BLACK HOLE storage engine.) .
The other interesting thing about the PostgreSQL PL language architecture is that it is a fairly thin wrapper around these languages.
This means the kind of code you write in those languages is pretty much what you would write if you were doing general programming
in those languages minus some spi calls. Since the handler is a just a thin wrapper around the environment, the language environment must be installed on the database server before you can use the PL language handler. This means you can have these functions utilized in your SQL statements and you can write
in a language you feel comfortable with if you can get the darn PL compiled for your environment or someone has already kindly compiled it for your environment or that it is even compilable for your environment. The pluggable PL architecture means you can
write a PL Handler for your favorite language or invent your own language that you can run in the database. In the end
the barrier between code,data, and semantic constructs is more of a constraint imposed by compilers. If you have any doubts about the above statement, you need only look at some javascript injection attacks
to bring the statement home. One of my fantasies is
developing a language that morphs itself, that utilizes the database as its morphing engine and its OS and that breaks the illusion of data being data, code being code, and lacks rigid semantics.
Of the languages we have worked with, SmallTalk comes closest to a language that satisfies these ideals and Lisp to a much lesser extent. Lisp lacked the semantic elegance of SmallTalk among other things.
Most people are used to having their procedural language push their data around. PL code living in PostgreSQL allows your data to push your procedural code around in a set-based way. This is a simple but pretty powerful feature since data is in general more fluid than code. For interpretated/just-in time compiled languages it can live in the database, for compiled it has to call compiled functions.
