🗄️ DBMS

Normalization, ACID, indexes and isolation — the subject interviewers use to find out whether you've only ever written SELECT statements.

ER modelling & keys

Entities, relationships, and the different kinds of key.

1NF through BCNF, and why the textbook goal isn't always achievable.

What each letter actually guarantees, and who enforces it.

The four levels, the three anomalies, and where real databases differ.

B+ trees, clustered vs non-clustered, and why more indexes isn't better.

The join types, and the three algorithms underneath them.

Locking, MVCC, and deadlock.

CAP, the four NoSQL families, and when the trade is worth it.

Reading these once won't hold

In the app these become flashcards on an expanding schedule, so you revisit each one just before you'd forget it.