One-to-Many, Many-to-Many — Relationships Between Tables
Master database relationships with foreign keys, junction tables, and real-world examples of one-to-one, one-to-many, and many-to-many patterns.
13 min readdatabases, sql, relationships, foreign-keys, schema-design
In the normalization lesson, we split one big table into several focused tables. But those tables don't exist in isolation — they're connected. A customer has orders. An order contains products. A product belongs to a category.
These connections are called relationships, and getting them right is the foundation of solid database design.
The Three Types of Relationships
Every relationship between two tables falls into one of three categories:
- One-to-One (1:1): One record in Table A relates to exactly one record in Table B
- One-to-Many (1:N): One record in Table A relates to multiple records in Table B
- Many-to-Many (M:N): Multiple records in Table A relate to multiple records in Table B
Let's look at each with real examples.
One-to-Many: The Most Common Re
This lesson is part of the Guild Member curriculum. Plans start at $29/mo.