Part of the "SQL: Zero to Ninja" series, written for junior web developers. You made a users table. You made an orders table. Now a real question hits you: how do these two tables actually know about each other? And while we are at it, why do senior devs freak out when you copy the same name into ten rows? Let me show you both, the easy way. The idea in one line Tables connect through relationships (one-to-many, many-to-many, one-to-one), and normalization just means: store each fact once, in one place, and point to it instead of copying it. The metaphor: your home address Imagine you send 50 letters this year. You could write your full home address on every single envelope, 50 times. But what happens when you move? Now you have 50 envelopes with the wrong address, and good luck fixing them all. Smart people do this instead: they keep their address in one address book, and everywhere else they just say "see my address book." Move once, fix once, done. That is the whole spirit of normalization.…