Find Unused Indexes in Oracle (DBA_INDEX_USAGE)

-- 12.2+ : DBA_INDEX_USAGE
SELECT i.owner, i.index_name, i.table_name, i.index_type,
       NVL(u.total_access_count, 0) AS total_access_count, u.last_used
FROM   dba_indexes i
LEFT JOIN dba_index_usage u ON u.owner = i.owner AND u.name = i.index_name
WHERE  i.owner NOT IN ('SYS','SYSTEM')
  AND  i.uniqueness = 'NONUNIQUE'
  AND  NVL(u.total_access_count, 0) = 0
ORDER  BY i.owner, i.table_name;