I have a task to migrate the existing enterprise geodatabase in ArcGIS 9.x to ArcGIS 10.x as part of the system migration. What is the practical way to do this? Can I just upgrade the database to ArcGIS 10.x or I really have to copy the whole database to a newer version using ArcSDE. Can you also share with me any blog sites or other materials that I can use using ArcSDE for this purpose.
there is no "one pratical way". What you have to do depends on your RDBMS, from the exact version, etc... Whether you can migrate directly or not depends on the initial version. If you have 9.2 or an earlier version you have to migrate to 9.3.1 first.
For setting up geodatabase in Oracle see http://desktop.arcgis.com/en/arcmap/10.3/manage-data/gdbs-in-oracle/setup-geodatabase-oracle.htm