A primary key uniquely identifies each row in a table. In relational databases, a primary key is often referenced by a foreign key in another table and used as the JOIN relationship.
Understanding primary keys makes it easier to identify reliable JOIN columns and understand table relationships.
CustomerID uniquely identifies a customer and is referenced by CustomerID in the Orders table.
SELECT
c.CustomerName,
o.OrderID
FROM Customers c
INNER JOIN Orders o
ON c.CustomerID = o.CustomerID;Used throughout relational databases for customers, employees, products, accounts, orders, and transactions.
- Primary keys uniquely identify rows.
- Primary keys are commonly used in JOIN relationships.
- Foreign keys often reference primary keys.
- Primary keys should provide reliable row identification.
- Correct key selection is critical for accurate JOINs.
Why are primary keys important in JOINs?
They provide a unique way to identify records and commonly serve as the parent side of table relationships.
Can a primary key contain duplicate values?
No. A primary key must uniquely identify each row.