A column of JSON data can be stored in the In-Memory Column Store (IM column store) to improve query performance.

• Overview of In-Memory JSON Data
  You can populate JSON data into the In-Memory Column Store (IM column store), to improve the performance of ad hoc and full-text queries.
• Populating JSON Data Into the In-Memory Column Store
  Use ALTER TABLE … INMEMORY to populate a column of JSON data, or a table with such a column, into the In-Memory Column Store (IM column store), to improve the performance of JSON queries.
• Upgrading Tables With JSON Data For Use With the In-Memory Column Store
  A table with JSON columns created using a database that did not have a compatibility setting of at least 12.2 or did not have max_string_size = extended must first be upgraded, before it can be populated into the In-Memory Column Store (IM column store). To do this, run script rdbms/admin/utlimcjson.sql.