MYSQL On Duplicate Key Do Nothing OR Insert If Not Exists

If you are looking for a MYSQL statement that essentially says 'on duplicate key do nothing' or 'insert if not exists', try:

INSERT IGNORE INTO ....

(from the manual)

If you use the IGNORE keyword, errors that occur while executing the INSERT statement are treated as warnings instead. For example, without IGNORE, a row that duplicates an existing UNIQUE index or PRIMARY KEY value in the table causes a duplicate-key error and the statement is aborted. With IGNORE, the row still is not inserted, but no error is issued. Data conversions that would trigger errors abort the statement if IGNORE is not specified. With IGNORE, invalid values are adjusted to the closest values and inserted; warnings are produced but the statement does not abort. You can determine with the mysql_info() C API function how many rows were actually inserted into the table.

You may also find http://bogdan.org.ua/2007/10/18/mysql-insert-if-not-exists-syntax.html good reading on the subject.