Problem Description
I had moved the SharePoint content databases from one farm to another recently. After the migration was completed I browsed to Central Administration -> Upgrade and Migration -> Review Database Status. The migrated SharePoint content database had the Status as "Database is in compatibility range and upgrade is recommended".
This indicated I had to manually upgrade these content databases.
Cause
This was because I moved the content databases from SharePoint 2010 SP1 to SharePoint 2010 SP2.
Resolution
Test-SPContentDatabase -Name ContentDBName-WebApplication http://webapp/ > c:\file1.txt (to confirm that there are no Upgrade Blocking categories that equal true)
Upgrade-SPContentDatabase ContentDBName (Depending on the size of the database, this process could take time.)
On seeing 100 % completion of database upgrade, browse to Central Administration -> Upgrade and Migration -> Review Database Status. Confirm that the content database now has Status as "No action required"
