Business Analyst: What is a primary key vs foreign key?

Primary key — unique identifier. Foreign key — link to another table.

Primary Key:

• Uniquely identifies each row.
• Cannot be NULL.
• Only one per table.

Foreign Key:

• References primary key in another table.
• Can be NULL.
• Multiple allowed.

Example:

1CREATE TABLE customers (
2  id INT PRIMARY KEY,
3  name VARCHAR(100)
4);
5
6CREATE TABLE orders (
7  id INT PRIMARY KEY,
8  customer_id INT,
9  FOREIGN KEY (customer_id) REFERENCES customers(id)
10);

BA relevance:

• Define data relationships.
• Ensure data integrity.
• Write requirements.