Use INSERT IGNORE rather than INSERT. If a record doesn't duplicate an existing record, MySQL inserts it as usual. If the record is a duplicate, the IGNORE keyword tells MySQL to discard it silently without generating an error.
Following example does not error out and same time it will not insert duplicate records.
mysql> INSERT IGNORE INTO person_tbl (last_name, first_name)
Use REPLACE rather than INSERT. If the record is new, it's inserted just as with INSERT. If it's a duplicate, the new record replaces the old one:
mysql> REPLACE INTO person_tbl (last_name, first_name)
INSERT IGNORE and REPLACE should be chosen according to the duplicate-handling behavior you want to effect. INSERT IGNORE keeps the first of a set of duplicated records and discards the rest. REPLACE keeps the last of a set of duplicates and erase out any earlier ones.