Can we upgrade reporting services to 2012 without having upgrading our instance of sql server. Just need to know compatibility.
Yes.
Create a Report Server Database
Database Server Version Requirements
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SQL Server is used to host the report server databases. The SQL Server Database Engine instance can be a local or remote instance. The following are the supported versions of SQL Server Database Engine that can be used to host the report server databases:
•SQL Server 2012
•SQL Server 2008 R2
•SQL Server 2008
•SQL Server 2005
Joie Andrew
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