I’m using the Feeds module to import lots of Feed Item nodes. Due to a malformed feed file, I’m getting lots of duplicates. I’m using a View to display these nodes, and need to be able to add a DISTINCT filter on the “Node: Post Date” field, so I only get 1 result for each post-date.
I will also look into tackling the problem at the source so to speak (I don’t want to have all those duplicates in the first place), but this is an interesting issue in itself – I can’t find a way to add a DISTINCT filter on a field other than the Node ID (which has it’s own option in the View’s Basic Settings box).
I found a great article on a good way to alter the SQL queries that are generated from views before they get executed: http://echodittolabs.org/blog/2010/06/group-views. I used this to basically suffix a GROUP BY clause to the end of the query (in a really nice, clean and versatile way).
As an aside, I also found a way to tackle the issue of importing lots of duplicate feed items, the details of which are here: http://drupal.org/node/661314#comment-3667228. It adopts quite an extreme approach (deleting all items before each update), but this is the only solution for some nasty malformed feeds.
I was holding out for some undiscovered feature of Views that let you do this, but I don’t think there is one – maybe in the next version 😉