No support for MySQL INSERT IGNORE.

[patrickt]

The idiomatic way to insert a record, falling back to a noop if the record is a duplicate, is to prepend the INSERT statement with IGNORE. I’m happy to take a shot at implementing this, though I might need a degree of guidance regarding the internals.

cc @tclem, who ran into this.

[tclem]

There are a couple of permutations of this. As an alternative to INSERT IGNORE you can also use REPLACE. It's also possible to define what to do on duplicate key with INSERT INTO .. VALUES .. ON DUPLICATE KEY UPDATE ...