Sql server 2008 r2 我无法连接SQL server数据库？

我在本地PC上安装了SQL server 2008R2（实例名称-SQLServer2008）和SQL server 2012（实例名称-MSSQLSERVER2012）

我可以使用SQL 2012登录

例如：

但和我尝试登录SQLServer2008R2的方式一样。（我尝试使用Windows身份验证和SQL Server身份验证登录，但无法登录。我遇到以下错误。）

例如：

错误：

A network-related or instance-specific errror occured while establishing a connection to sql server. The server was not found or was not accessible. Verify that the instance namme is correct and that SQL Server is configured to allow remote connections, (provider: SQL Network Interfaces, error: 25 connection string is not valid) (Microsoft SQL server, Error: 87)

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错误状态

连接字符串无效

，那么您的连接字符串在哪里？很抱歉，我不理解您的问题。因为我尝试仅使用SQL server Management studio登录。

server Name : .\SQLServer2008
Authentication : SQL server Authentication
User name : sa
password  : test123

A network-related or instance-specific errror occured while establishing a connection to sql server. The server was not found or was not accessible. Verify that the instance namme is correct and that SQL Server is configured to allow remote connections, (provider: SQL Network Interfaces, error: 25 connection string is not valid) (Microsoft SQL server, Error: 87)