每个MSSQL服务器实例都在其自己的端口号上运行. 您可以将MSSQL Server实例配置为使用固定端口号，而不使用动态端口号(这是默认端口号).

Every MSSQL server instance runs on its own port number. You can configure the MSSQL Server instance to use a fixed port number instead of a dynamic one (which is the default).

配置了固定端口后，您只需使用PDO连接到该端口号即可.不再需要在dsn或任何其他设置中引用该实例.

Once you've configure a fixed port, you can simply connect to that port number using PDO. There is no further need to reference the instance in the dsn or any other setting.