Database design

What it is

Schema design makes relationships and integrity explicit.

When to use it

Choose keys, constraints, and indexes from access paths and business rules.

Syntax

PK + FK + NOT NULL + UNIQUE + CHECK + targeted indexes

Example

orders.user_id -> users.id
orders.reference UNIQUE
orders.total_cents NOT NULL
index orders(user_id, status, id)
Deletion: restrict settled financial history.

Common mistakes

Application validation alone cannot ensure integrity; avoid premature denormalization.

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