I Built a Recommendation Engine in Pure Postgres. The Embeddings Lost to ORDER BY count(*).

Everyone reaches for an AI vector database to build 'people also bought.' I did too — then measured it on real Amazon data and watched the fancy approach lose to a few lines of SQL that just count what customers actually buy together. Here's the honest, plain-English comparison: what wins, what doesn't, and why you probably don't need the extra infrastructure — all in one database.