02 — Tables and Relationships

Core structure

• A relational database is made of tables; each table has rows (records) and columns (fields) 0:25.
• Example: a users table with columns id, name, email, and an orders table with its own id 0:55.
• A foreign key in one table is what connects it to another table (e.g., orders pointing back to users) 0:55.

Relationship types

• One-to-one — a direct one-to-one mapping between rows 0:55.
• One-to-many 0:55.
• Many-to-many — the one people most often get confused by 0:55.

erDiagram
    USERS ||--o{ ORDERS : "has (one-to-many)"
    USERS {
        int id PK
        string name
        string email
    }
    ORDERS {
        int id PK
        int user_id FK
    }