When it comes to stored procedures and functions, PostgreSQL differs quite significantly from other database systems. Most database engines force you to use a certain programming language to write server-side code. Microsoft SQL Server offers Transact-SQL, while Oracle encourages you to use PL/SQL. PostgreSQL doesn't force you to use a certain language; instead, it allows you to decide on what you know and like the best.
The reason PostgreSQL is so flexible is actually quite interesting in a historical sense, too. Many years ago, one of the most well-known PostgreSQL developers, Jan Wieck, who had written countless patches back in its early days, came up with the idea of using Tool Command Language (Tcl) as the server-side programming language. The trouble was that nobody wanted to use Tcl and nobody wanted to have this stuff in the database engine. The solution to the problem was to make the language interface so flexible that basically any...