Procedural languages aren't built into the
PostgreSQL server; they are offered
by loadable modules. Please refer to the documentation of the
procedural language in question for details about the syntax and how the
function body is interpreted for each language.
There are currently four procedural languages available in the
standard PostgreSQL distribution:
PL/pgSQL, PL/Tcl,
PL/Perl, and
PL/Python.
Refer to Chapter 36 for more information.
Other languages can be defined by users.
The basics of developing a new procedural language are covered in Chapter 47.