Register the New Functions

Now that you have created a dynamically linkable object file, you must register its functions with POSTGRESQL. The CREATE FUNCTION  command registers a new function by storing information in the database. Figure  shows the CREATE FUNCTION  command for ctof.  

        test=> CREATE FUNCTION ctof(float)
        test-> RETURNS float
        test-> AS '/users/pgman/sample/ctof.so'
        test-> LANGUAGE 'C';
        CREATE  

The function ctof takes a float argument and returns a float. The SQL data type float is the same as the C type double used in ctof(). The dynamically linkable object file is specified as /users/pgman/sample/ctof.so and is written in the C language.

A single object file can contain many functions. You must use CREATE FUNCTION to register each function you want to access from POSTGRESQL. CREATE FUNCTION  also allows nonobject files to be used as functions (see Chapter ).

Once the functions are registered, they can be called just like POSTGRESQL internal functions. Figure  shows the ctof() function used in a SELECT statement.  

        test=> SELECT ctof(20);
         ctof 
        ------
           68
        (1 row)  

See CREATE_FUNCTION for more information.