sync 2 tables in a single database in mysql with no duplicacy

I have 2 tables in a single database of MySQL.

The structures are like this:

mysql> desc main_tbl; +-----------------+--------------+------+-----+-------------------+----------------+ | Field | Type | Null | Key | Default | Extra | +-----------------+--------------+------+-----+-------------------+----------------+ | mid | int(11) | NO | PRI | NULL | auto_increment | | acc | varchar(255) | NO | MUL | NULL | | | device | varchar(255) | NO | | NULL | | | start | datetime | NO | | NULL | | | end | datetime | NO | | NULL | | | login_user | varchar(255) | NO | | NULL | | | date_added | datetime | NO | | CURRENT_TIMESTAMP | | +-----------------+--------------+------+-----+-------------------+----------------+

mysql> desc report_backup; +--------------+--------------+------+-----+-----------+----------------+ | Field | Type | Null | Key | Default | Extra | +--------------+--------------+------+-----+-----------+----------------+ | rid | int(11) | NO | PRI | NULL | auto_increment | | mid | int(11) | NO | UNI | NULL | | | times | varchar(255) | NO | | 2 minutes | | | account | varchar(255) | NO | | NULL | | | dev | varchar(255) | NO | | NULL | | | start | datetime | NO | | NULL | | | end | datetime | NO | | NULL | | | logged_user | varchar(255) | NO | | NULL | | | added_time | datetime | NO | | NULL | | +--------------+--------------+------+-----+-----------+----------------+

The first table is populated with user input, where records can be added,deleted.

The second table is used for backup where whenever a record is inserted in the 1st one, it will be automatically copied.

So I used a query like this to run everytime any record is inserted in the 1st table;

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;

But this seems not working due to the mid is unique, which I made to avoid duplicate entry.

Any suggested solution will be appreciated.

Thanks