Number of sites are zero after upgrade using database migration technique.
Each site collection in a content database (including each portal site) has a globally-unique identifier (GUID) associated with it, registered in the configuration database. So, adding the same site collection (or portal) twice to the farm, even in separate Web applications, is not possible. Although the database attach succeeds in this situation, the site collection cannot be started. If you need a duplicate copy of a site collection (or portal) in the same farm, first attach the database that contains the site collection to a separate farm, and then use the Stsadm.exe backup and restore operations to copy the site collection over to the other farm. The backup and restore process creates a new GUID for the site collection.
Saved my life 🙂