Search for authors whose records are separated by at least X days I am using Postgres and have a table which contains metadata about several million images - many of which have the same author. 

I am looking for contributors who add content regularly - not people who add images in "bursts" of many photos in a short period of time. In other words, I'd rather people who post six photos over a matter of months than 12 photos in just one week, but never post outside that short time window.

Writing a statement like SELECT count(*) AS i_count,author_id FROM images GROUP BY author_id ORDER BY i_count DESC will give me a list in descending order of who has contributed the most photos to the least, but how might I be able to select only people who have contributed images in a period that is greater than 30 days?

I have a date_added column as well.
A check in the HAVING clause would do the trick:

SELECT author_id, count(*) AS i_count
FROM   images
GROUP  BY author_id
HAVING max(date_added) &gt; min(date_added) + interval '30 days'
ORDER  BY i_count DESC;