In your case, on your OLD server, FIRST add a DBSERVER to the dbservers tab pointing to a version of SQL-server that is supported by BOTH QC11 and QC12.x (SQL-SERVER 2008 R2/SP2 -- explicitly).
Then in your OLD server, make individual project COPIES where the resulting copy has a new/unique name AND you indicated SQL-Server as the target DB location.
When all of your projects are in SQL-Server, you can easily upgrade them as explained in the QC12.20 Installation/upgrade documentation..
As for the main QC database that keeps track of the users and list of projects (qcsiteadmin_db), there is NO easy way to convert that from ORA to SQL-server. so you must start over with that.
You can indicate to create a NEW one during 12.2 install, then when you RESTORE each project, it will add the users that were using that project into your ''global'' user list in Site admin -- but they will all have BLANK passwords and no email addresses or other user info.
Your project tree will also be empty -- you will need to re-create all domains (other than ''Default'') -- pay attention to the corresponding repository folder for the domain as when you migrate the project repositories they will need to be placed into the CORRECT/new domain folder and their respective DBID.XML files edited to reflect the NEW ''project directory'' path (you have to do this anyway as the old path was in Unix).
An alternative to all of this (keeping ORACLE) would be to make sure your ORACLE instance is one supported by ALM12.2 (you should probably migrate Schemas to a NEW instance separate from one used by QC11). You could install QC/ALM12.20 and indicate for it to UPGRADE a copy of the qcsiteadmin_db schema (this would keep the users and project tree). Then, all you would need to do is migrate the repositories to the Windows server location, edit DBID's and you can just RESTORE/VERIFY/REPAIR/UPGRADE the projects. -- NOW you would still be on ORACLE for the back-end - but your user/info would still be intact.