In theory you could use timestamps that go back in time for this CF. That way the first write will persist over future writes.
On Sep 21, 2010, at 6:58 AM, Christian Decker <decker.christ...@gmail.com> wrote: > Hi all, > > I have a rather strange problem I'd like to address. As I understand it a > write in cassandra always overwrites already existing data, so it is not > possible to have a way to create an index pointing to the first entry > matching some criteria. What I mean is that I have a CF which stores user > purchases and now I want to find the first time a user bought an item from a > certain class of objects. For this I was thinking about a CF with SCFs, the > CF key being the user ID and the SCF key being the class id of the item and > then the value would be the key of the purchase in the purchases CF. > Obviously for this to work I'd have to check if a value like > firstPurchases[123][987] already exists and if not write it, but it there a > way to implement it without the additional read? > > Regards, > Chris
