WordPress Update Meta Key

gistfile1.aw

<?php

/**
 * Rename meta keys
 * Usage: update_meta_key( 'old_key', 'new_key');
 */
function update_meta_key( $old_key=null, $new_key=null ){
    global $wpdb;

    $query = "UPDATE ".$wpdb->prefix."postmeta SET meta_key = '".$new_key."' WHERE meta_key = '".$old_key."'";
    $results = $wpdb->get_results( $query, ARRAY_A );

    return $results;
}

Please don't do this. It's vulnerable to SQL injection attacks. Please use $wpdb->prepare() to escape input parameters.