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407. JOIN Using Primary Key

Understand how primary keys can be used to connect related tables.

📘 Lesson 417 of 728 ⏱ 10 min 🎯 Intermediate

A primary key uniquely identifies each row in a table and can be used as a reference point when joining that table with related data.

Primary keys provide reliable identifiers for records and are fundamental to accurate table relationships.

Join Customers and Orders using CustomerID as the customer identifier.

SQL 
SELECT
    c.CustomerName,
    o.OrderID
FROM Customers c
INNER JOIN Orders o
    ON c.CustomerID = o.CustomerID;

Primary-key-based joins are common across customer, employee, product, account, transaction, and order systems.

  • Primary keys uniquely identify rows.
  • Primary keys can participate in joins.
  • Related tables often reference primary keys.
  • Good keys help prevent ambiguous relationships.
  • Joins should use logically related columns.
Why are primary keys important for joins?

They provide unique identifiers that help establish reliable relationships between records.

Can a primary key be used in multiple joins?

Yes. A primary key can participate in relationships with multiple related tables.

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