That's true for keys, but that really only covers a subset of what JOINs can do -- if I want to use things like dates, times, quantities of things... and frankl

That's true for keys, but that really only covers a subset of what JOINs can do -- if I want to use things like dates, times, quantities of things... and frankly, if I want to do something other than JOIN on equal values, say join on greater or less than or between, then that's an entirely different thing altogether.