ช่วยดู Code PHP หน่อยคับ mysql_fetch_assoc(): supplied argument is not a valid MySQL result resource

<?php

//user from table
function fetch_users(){
	$result = mysql_query('SELECT `user_id` AS `id`, `user_username` AS `username` FROM `users`');
	
	$users = array();
	
	while (($row = mysql_fetch_assoc($result)) !== false){
		$users[] = $row;
	}
	
	return $users;
}

//profile information
function fetch_user_info($uid){
	$uid = (int)$uid;
	
	$sql = "SELECT
			     `user_username` AS `username`,
				 `user_password AS `password`,
				 `user_name` AS `name`,
				 `user_email` AS `email`,
				 `user_about` AS `about`,
				 `user_status` AS `status`
			FROM `users`
			WHERE `user_id = {$uid}";
			
			$result = mysql_query($sql);
			
			return mysql_fetch_assoc($result);
}

?>