Parsing error

Hi every one

I have a big problem, I think it's a syntaxical one, but can't solve it,
please help !

What I am trying to do is a simple function who updates data in a table and
if no row was updated, then add a new one with the specified parameters.
And i would like to do it using SQL and anything else.

Below is the screen shot from psql (I run postgresql-7.1.2-4PGDG )

[~/pgsql/test]$ psql ze_database ze_user
Welcome to psql, the PostgreSQL interactive terminal.

Type: \copyright for distribution terms
\h for help with SQL commands
\? for help on internal slash commands
\g or terminate with semicolon to execute query
\q to quit

ze_database=> CREATE TABLE my_table (
ze_database(> p1 integer,
ze_database(> p2 integer,
ze_database(> p3 integer,
ze_database(> p4 integer);
CREATE
ze_database=> CREATE FUNCTION my_add(integer,integer,integer,integer)
ze_database-> RETURNS integer
ze_database-> AS 'INSERT INTO my_table VALUES ($1,$2,$3,$4); SELECT 1'
ze_database-> LANGUAGE 'sql';
CREATE
ze_database=> CREATE FUNCTION my_update(integer,integer,integer,integer)
ze_database-> RETURNS integer
ze_database-> AS 'SELECT CASE WHEN UPDATE my_table SET p1= $1, p2= $2 WHERE
p3= $3 AND p4= $4 ~* \'UPDATE 0\' THEN my_add($1,$2,$3,$4) ELSE 1 END'
ze_database-> LANGUAGE 'sql';
ERROR: parser: parse error at or near "my_table"
ze_database=>

I don't see my error, can anyone open my eyes and correct me, please help

Thanks in advance