Business analysis glossary
Primary Key
What it is
A primary key is a column, or combination of columns, whose value uniquely identifies each row in a table. It cannot be empty and cannot repeat. It is often a generated number such as order_id, but it can also be a natural identifier, as long as it is truly unique and stable.
Why it matters
Reliable keys let you find, update and join records without confusing two different things. Misunderstanding keys is a common cause of wrong counts and duplicated rows in reports. A key also lets analysts spot duplicate rows quickly, by checking whether the key appears more than once when it should not.
Example
In the Orders table at Marlow Online Store, order_id is the primary key: 10452 refers to exactly one order. Customer name could not be the key because two different customers can share a name. Counting rows by order_id rather than by a repeated value avoids reporting the same order twice.