Oracle 11g Enterprise downgrade to Standard One I'm checking possibilty of downgrade Oracle 11g from Enterpise Edition to Standard One edition. I've cross-checked edition comparison with 

select name from dba_feature_usage_statistics where currently_used='TRUE'


Query result from dba_feature_usage_statistics:

Job Scheduler
Oracle Java Virtual Machine (user)
Oracle Java Virtual Machine (system)
Automatic Memory Tuning
Oracle Utility Metadata API
Segment Advisor
Automatic SQL Tuning Advisor
Object
Materialized Views (User)
Audit Options
Automatic Maintenance - Optimizer Statistics Gathering
Automatic Maintenance - Space Advisor
Automatic Maintenance - SQL Tuning Advisor
Automatic Segment Space Management (system)
Automatic Segment Space Management (user)
Automatic Undo Management
Client Identifier
Character Set
Locally Managed Tablespaces (system)
Locally Managed Tablespaces (user)
Parallel SQL Query Execution
Partitioning (system)
Recovery Area
Recovery Manager (RMAN)
RMAN - Disk Backup
Backup BASIC Compression
Logfile Multiplexing
Server Parameter File
Shared Server
Streams (user)
LOB
SecureFiles (system)


I think Parallel SQL Query Execution and Partitioning (system) are only in Enterprise Edition, but I'm not sure about rest, especially:

Automatic Memory Tuning
Segment Advisor
Automatic SQL Tuning Advisor
Automatic Maintenance - SQL Tuning Advisor
Recovery Area


Do you guys know which edition of Oracle is needed to use these features?
Ultimate source for such answers is Oracle Database Licensing Information.

Sadly to downgrade from Enterprise to Standard Edition you have to export all the data install Oracle Standard Edition and import data (Doc ID 139642.1).

From your list "Automatic SQL Tuning Advisor" is Enterprise Edition only feature. As a rule of thumb - features which needs AWR are Enterprise Edition only plus you need to buy Oracle Diagnostics Pack.