JOIN combines related information horizontally by adding columns from different tables, while UNION combines compatible result sets vertically by adding rows.
Understanding this difference prevents choosing the wrong SQL operation when combining data.
Use JOIN to combine customer and order information, and UNION to combine customer records from two compatible sources.
SELECT
c.CustomerName,
o.OrderAmount
FROM Customers c
INNER JOIN Orders o
ON c.CustomerID = o.CustomerID;Common in reporting, data integration, migrations, and combining historical datasets.
- JOIN combines related columns.
- UNION combines rows from result sets.
- JOIN requires a relationship between datasets.
- UNION requires compatible column structures.
- UNION and JOIN solve different problems.
What is the difference between JOIN and UNION?
JOIN combines related tables horizontally, while UNION combines compatible result sets vertically.
Does UNION require a matching key?
No. UNION does not require a relationship key; the result sets must have compatible columns.