php 싱글쿼테이트

http://php.net/manual/en/tutorial.forms.php 
http://php.net/manual/en/language.variables.superglobals.php 
http://php.net/manual/en/function.mysql-error.php

http://php.net/manual/en/language.types.string.php 
http://php.net/manual/en/language.types.array.php