One optimization is to write big O notation in minimized form. It looks more impressive to write O(n). And to try being helpful: do aggregation in the db where

One optimization is to write big O notation in minimized form. It looks more impressive to write O(n). And to try being helpful: do aggregation in the db where possible, be sure indexes are good, play around with the number of rows you process at a time, use joins if appropriate to minimize queries, if your queries are expensive at all use EXPLAIN, depending on the database, look into using a cursor (maybe?).