Syntax:
VALUES(col_name)

In an INSERT ... ON DUPLICATE KEY UPDATE statement, you can use the
VALUES(col_name) function in the UPDATE clause to refer to column
values from the INSERT portion of the statement. In other words,
VALUES(col_name) in the UPDATE clause refers to the value of col_name
that would be inserted, had no duplicate-key conflict occurred. This
function is especially useful in multiple-row inserts. The VALUES()
function is meaningful only in INSERT ... ON DUPLICATE KEY UPDATE
statements and returns NULL otherwise.
http://dev.mysql.com/doc/refman/4.1/en/insert-on-duplicate.html.
