Mastering PostgreSQL 12 - Third Edition

The anatomy of a function

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.

Note that the code of the function is passed to PostgreSQL as a string ('). This is somewhat noteworthy because it allows a function to become a black box to the execution machinery.

In other database engines, the code of the function is not a string, ...