Database Management

Making a static recommender respond to the shopper, when the median visitor has viewed exactly one product and left.

Content-based recommendations for a jewelry catalog with no click data to learn from. TF-IDF in SQL, why grouping products is a graph problem, and a sliding carousel built with no JavaScript at all.

Same query, same code, a thousand times faster. How a B-tree index lets the database skip reading the whole table, what it costs you on writes, and how EXPLAIN tells you where one actually belongs.