NULL can mean a bunch of things: 1. Value is unknown 2. Value does not exist (for example, outer join results). These have ery different implications. For

NULL can mean a bunch of things: 1. Value is unknown 2. Value does not exist (for example, outer join results). These have ery different implications. For example: somestring || does_not_exist you would think would equal somestring, but with unknown we dont know.