Requirements for Win32 platforms. The extension requires the MS SQL Client Tools to be installed on the system where PHP is installed. The Client Tools can be installed from the MS SQL Server CD or by copying ntwdblib.dll from \winnt\system32 on the server to \winnt\system32 on the PHP box. Copying ntwdblib.dll will only provide access. Configuration of the client will require installation of all the tools.
请将ntwdblib.dll置于系统搜索路径中一般的说,安装sql server客户端是较好的做法