php 依赖注入。PHP 点滴疑惑

1. 在数据库中，字段为NULL,可以使用empty()进行判断

   <?php $CONFIG['hostname'] = 'localhost';$CONFIG['username'] = 'root';$CONFIG['password'] = '';$CONFIG['database'] = 'test';$link = mysql_connect("localhost", $CONFIG['username'], $CONFIG['password']);mysql_select_db($CONFIG['database'], $link );$charset = mysql_query("SET NAMES 'utf8'", $link);$sql = "select init_weight from mytableas where id=3948";$query = mysql_query($sql);var_dump(mysql_fetch_assoc($query));$init_weight = mysql_fetch_assoc($query);var_dump(empty($init_weight['init_weight']));
   ?>