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447. JOIN on Multiple Columns

Learn how to match records using more than one column in a JOIN condition.

📘 Lesson 447 of 728 ⏱ 11 min 🎯 Intermediate

A multi-column JOIN uses two or more columns together to determine whether records from two tables correspond.

Some relationships cannot be uniquely identified using a single column.

Match records using both EmployeeID and DepartmentID.

SQL 
SELECT
    a.EmployeeID,
    a.DepartmentID,
    a.Salary,
    b.Salary AS PreviousSalary
FROM CurrentSalary a
INNER JOIN PreviousSalary b
    ON a.EmployeeID = b.EmployeeID
   AND a.DepartmentID = b.DepartmentID;

Multi-column joins are useful for composite keys, regional data, historical records, and systems where a single identifier is not sufficient.

  • JOIN conditions can contain multiple columns.
  • AND is commonly used between conditions.
  • Multiple columns can form a composite key.
  • All required matching conditions should be included.
  • Missing a condition can create incorrect matches.
Can a JOIN use multiple columns?

Yes. A JOIN can use multiple columns in its matching condition.

Why might multiple columns be needed?

Multiple columns may be required when one column alone does not uniquely identify the relationship.

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