Mysql--insert into ... On DUPLICATE KEY UPDATE ...

Transferred from: https://my.oschina.net/iceman/blog/53735

If an on DUPLICATE KEY UPDATE is specified at the end of the INSERT statement, and the row is inserted, it causes duplicate values to appear in a unique index or primary KEY.

The update is performed on the row where duplicate values occur;

If the problem does not cause the unique value column to repeat, insert a new row.

Note: On DUPLICATE KEY update is only a unique syntax for MySQL, not SQL standard syntax!
This syntax and suitability is used in scenarios where it is necessary to determine whether a record exists or not, and the insertion exists.

Mysql--insert into ... On DUPLICATE KEY UPDATE ...