How do you define a primary key when creating a table?

Difficulty: 3/10

primary key syntax, auto_increment, composite keys

Defining Primary Keys in MySQL

A primary key is a column (or a group of columns) that uniquely identifies each row in a table. It ensures no two rows have the same primary key value and that the column(s) cannot contain NULL.

1. Why Primary Keys Are Important

1
Ensure each row is uniquely identifiable.
2
Improve query performance using indexes created automatically.
3
Prevent duplicate or NULL values in the key column.
4
Enable relationships with foreign keys in other tables.

2. Ways to Define a Primary Key

1
Define it inline with the column.
2
Define it separately at the table level.
3
Use composite (multi-column) primary keys.

Example 1: Inline Primary Key Definition

Example 2: Table-Level Primary Key Definition

Example 3: Composite Primary Key

Composite primary keys enforce uniqueness across a combination of columns instead of a single column.

Scenario Questions

0-2 years experience

Follow-up Questions