update or insert if necessary?

[steve]

I have a situation where I need to update a record for a given key in a MySQL table, but
insert a record if the key doesn't exist.  I could do this by doing a SELECT on the key,
then doing an UPDATE if anything comes back, or and INSERT otherwise.  This seems rather
clunky though, and I'm wondering if there is anything like and "up-sert" command, or at
least a preferred way of doing this operation.

TIA....Steve