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: 當安全模式開啟,PHP會檢查執行的腳本和要操作的檔案或目錄是否有相同的UID(擁有者)。