Conditional on duplicate key update

gistfile1.sql

# A simple example which assumes you have an ENUM('auto', 'manual') column "override" in your table. 

INSERT INTO
    foo( id, baz, bar )
VALUES
    ( ?, ?, ? )
ON DUPLICATE KEY UPDATE
    baz = IF(override = 'auto', VALUES( baz ), baz),
    bar = IF(override = 'auto', VALUES( bar ), bar);