Before we dig into a specific language, we will look at the anatomy of a typical function. For demonstration purposes, let's look at the following function, which just adds two numbers:

test=# CREATE OR REPLACE FUNCTION mysum(int, int)  
RETURNS int AS 
' 
  SELECT $1 + $2; 
' LANGUAGE 'sql';  
CREATE FUNCTION 

The first thing to observe is that this function is written in SQL. PostgreSQL needs to know which language we are using, so we have to specify that in the definition.

In other database engines, the code of the function is not a string, but is directly attached to the statement. This simple abstraction layer is what gives the PostgreSQL function manager all its power. Inside the string, you can basically use all that the programming language of your choice has to offer.

In this example, we will simply add up two numbers that have been passed to the function. Two integer variables are in use. The important part here is that PostgreSQL provides you with function overloading. In other words, the mysum(int, int) function is not the same as the mysum(int8, int8) function.

PostgreSQL sees these things as two distinct functions. Function overloading is a good feature; however, you have to be very careful not to accidentally deploy too many functions if your parameter list happens to change from time to time. Always make sure that functions that are not needed anymore are really deleted.

Let's run the mysum function:

test=# SELECT mysum(10, 20); 
 mysum 
------- 
 30  
(1 row) 

The result here is 30, which is not really surprising. After this introduction to functions, it is important to focus on the next major topic: quoting.