sync 2 tables in a single database in mysql with no duplicacy
The mysql Syntax for insert data is :

INSERT INTO table_name ( field1, field2,...fieldN )
                       VALUES
                       ( value1, value2,...valueN );


In your query you just missed values and you must pass where condition to select a specific row, in your case the last insert id:

 INSERT INTO report_backup(mid, account, dev, start, end, logged_user, added_time) SELECT mid, acc, device, start, end, login_user, date_added from main_tbl;

Correct one is :

INSERT INTO report_backup(mid, account, dev, start, end, logged_user, added_time) VALUES (SELECT mid, acc, device, start, end, login_user, date_added from main_tbl WHERE mid = 'Your Last Inserted Value');


Hope my answer is clear enough to fix your issue.