Sqoop export upsert not working for table with no primary key

sqoop

#1

I have two tables orders_test and orders_csm of same schema as orders table in retail_db. Exception is orders_csm doesn’t have order_id as primary key.
Then, I run sqoop export with --update-key as order_id and --update-mode as allowinsert, to update back changes in order_status to both order_csm and order_test tables.
I found, order_test table updated with the updated columns but in orders_csm (no primary key) table additional rows from the --target-dir are inserted and no update happened.

Can anyone help me to understand why there are different behavior for the export command in case of table with no primary key?

RDBMS I am using is mysql.