We all know that SQL Server can have 1 default instance & many named instance.

But I want to check, How SQL Server Setup behave, If I tries to use instance name that is already being used by some existing SQL server on my system.

I am already having 2 instances running on my system, 1 SQL Server 2008 & 1 SQL Server 2012.

I must say, SQL Server setup is too cleaver. It shows me that instance that use the name (passed by me) & show me a SQL server version of that instance as well.

In same way, It works for both default & Named instance.

1) While installing 3rd instance of SQL Server 2005, I pass the instance name used by SQL Server 2008.

2) While installing 3rd instance of SQL Server 2005, I pass the instance name used by SQL Server 2012.