INSERT ON DUPLICATE KEY UPDATE and REPLACE INTOJonathan Haddad writes about REPLACE INTO and INSERT ON DUPLICATE KEY UPDATE. Really, Why MySQL has both of these, especially both are non ANSI SQL extensions ? The story here seems to be the following – REPLACE INTO existed forever, at least since MySQL 3.22 and was a way to do replace faster and what is also important atomically, remember at that time MySQL only had ISAM tables with table locks
