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Primary Keys and Foreign Keys - Building Block - Databases (SQL) | System Design Interview Prep | Repovive

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System Design Interview Prep22 sections · 691 units23h total

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Primary Keys and Foreign Keys

Relationships between tables

Primary key: Uniquely identifies a row. Usually an auto-incrementing integer or UUID. Every table needs one.

Foreign key: References a primary key in another table. Enforces referential integrity.

users: id (PK), name, email
orders: id (PK), user_id (FK → users.id), total
order_items: id (PK), order_id (FK → orders.id), product_id, quantity

Foreign keys prevent orphaned records. You can't delete a user who has orders (unless you cascade delete or set null).