Returns a dbase_identifier for the opened database, or FALSE if the database couldn't be opened.
Parameter flags correspond to those for the open() system call (Typically 0 means read-only, 1 means write-only, and 2 means read and write).
注: 当 安全模式（safe mode） 被激活，PHP 将检查您将要操作的文件或者目录与正在执行的脚本是否有相同的 UID。