[RESOLVED] logic for (INSERT if row does not exist) else (UPDATE if row exists)

[cretaceous]

hi - is there a logic structure I can use to INSERT a row if UPDATE finds no row?
and I dont mean the standard if id business...

its a page with an iterative set of text inputs based on dates so has a looping UPDATE running off a "foreach"

the dates are set elsewhere and this page shows input fields (for prices) for each date - so that's not a fixed number of fields
- I can get the values for the inputs and have them ready to add to to db but I'm not sure of how to add a new one to the database -

lets say someone adds "Jan 28 2009"
how do I tell the system to INSERT and not UPDATE - I'm not sure what to be searching on for clues!

I guess I can feed my input form with values for "if row found" like the normal insert/update logic?
is there a better way?

[cretaceous]

ok it was a stupid question - do it with id, more hidden inputs and another array