Converting a managed non-transactional table to external
You can easily convert a managed table, if it is not an ACID (transactional) table, to external using the ALTER TABLE statement. You might have a non-ACID, managed table after an upgrade from Hive 1 or 2.
The following pseudo-code changes a managed table, if it is not transactional, to external. The data and metadata is dropped when the table is dropped.
ALTER TABLE ... SET TBLPROPERTIES('EXTERNAL'='TRUE','external.table.purge'='true')