> And why do people freak out when they see a JOIN? It's one of the simplest concepts in databases: intersecting two sets. Everything in column A that matches e

> And why do people freak out when they see a JOIN? It's one of the simplest concepts in databases: intersecting two sets. Everything in column A that matches everything in column B. Actually no, that's not what a join is. A join is a cartesian product (not an intersection), followed by a WHERE clause (which doesn't have to be an exact match of a value between columns). This is further complicated by outer joins where empty rows are added to one or both of the sets involved in the cartesian product.