Functional Dependencies
A functional dependency X → Y means knowing X determines Y. Understanding FDs is the foundation for all normal forms.
MySQL
Intermediate
4 min read
Functional Dependencies
Example
-- In an orders table:
-- order_id -> customer_id (each order has one customer)
-- order_id -> total (each order has one total)
-- customer_id -> customer_name (each customer has one name)
-- Transitive: order_id -> customer_id -> customer_name
-- This transitive dependency violates 3NF Pro Tip
Draw an arrow diagram of all FDs to spot normalization violations visually.