SQL Server opens database files with exclusive access. This is necessary because SQL Server manages the locking of the database data in its memory. Thus, if more than one SQL Server instance has the same file open, there is the potential for data corruption. If two different user instances use the same database file, one instance must close the file before the other instance can open it. There are two common ways to close database files, as follows.
1. User instance databases have the Auto Close option set so that if there are no connections to a database for 8-10 minutes, the database shuts down and the file is closed. This happens automatically, but it can take a while, especially if connection pooling is enabled for your connections.
2. Detaching the database from the instance by calling sp_detach_db will close the file. This is the method Visual Studio uses to ensure that the database file is closed when the IDE switches between user instances. For example, you are using the IDE to design a data-enabled Web page. You press F5 to run the application. The IDE detaches the database so that ASP.NET can open the database files. If you leave the database attached to the IDE and try to run the ASP page from your browser, ASP.NET cannot open the database because the file is still in use by the IDE.