How to use ON DUPLICATE KEY UPDATE in Postgresql with php

PHP
3

ok so how do i work out this problem:

i am trying to catch this error in a php webapp that captures input
data from a user. im using php and pgsql on mypgadmin, sourcecode column
constraints : “CONSTRAINT sourcecodes_sourcecode_key UNIQUE (sourcecode)”

ERROR

Warning: pg_execute() [function.pg-execute]: Query failed: ERROR:
duplicate key value violates unique constraint
“sourcecodes_sourcecode_key” DETAIL: Key (sourcecode)=(Source3) already
exists. in D:\xampp\htdocs …php on line 289

Problem when user enters an existing sourcecode then the error is generated on POSTING the value.

Code

if(array_key_exists(“btnsubmit”, $_POST)) {
$pk_check = “true”;

if($pk_check == "true") {
    $parameters = array();
    $parameters[] = $counter;

    $parameters[] = $_POST['source'];


    $sql_string = "INSERT INTO config.sourcecodes (id,sourcecode ) VALUES ($1,$2 )";


    try {
        $saved = $db_cfg->Execute($sql_string, "", $parameters);


        if($saved) {
            $feedback = 'New Campaign: ' . $_POST['campaign_id'] . ' Saved  successfully';
        } else {
            error_reporting(32);
            $feedback = "_Error Saving Source Code ! _";
            //echo pg_last_notice($sql_string) ;
            //  throw new $exception('Error saving new source code');
        }
    }
    catch(\sdException $exception) {
        throw new Exception('fatal err trycatch nt wrkn');
    }