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408. JOIN Using Foreign Key

Understand how foreign keys connect records in related database tables.

📘 Lesson 418 of 728 ⏱ 10 min 🎯 Intermediate

A foreign key is a column or set of columns that references a key in another table, commonly a primary key, and is often used as the join column between related tables.

Foreign keys represent relationships between business entities and make it possible to combine related information accurately.

Orders can contain CustomerID as a foreign key referencing Customers.CustomerID.

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

Foreign-key relationships are common in banking, e-commerce, HR, insurance, healthcare, and financial systems.

  • Foreign keys represent relationships between tables.
  • A foreign key commonly references a primary key.
  • Foreign keys are frequently used in JOIN conditions.
  • One customer can have many orders.
  • Foreign-key relationships support relational database design.
What is a foreign key?

A foreign key is a column or group of columns that references a key in another table.

Why are foreign keys useful in SQL joins?

They provide a logical relationship that allows related records from different tables to be connected.

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