📝 What You’ll Learn

• What UNION does
• Syntax and structure
• Examples of using UNION
• Difference between UNION and UNION ALL

🔄 What Is UNION?

The UNION operator in SQL is used to combine the result sets of two or more SELECT queries into a single result set.

• It eliminates duplicate rows by default.

It’s useful when you need to combine data from similar tables or queries with the same structure.

🧱 UNION Syntax

SELECT column1, column2, ...
FROM table1
UNION
SELECT column1, column2, ...
FROM table2;

🧪 Example: Combine Customers from Two Regions

SELECT name, region
FROM customers_east
UNION
SELECT name, region
FROM customers_west;

This query combines the customers from the East and West regions into a single list, excluding duplicates.

🧪 Example: Combine Products and Services

SELECT product_name AS item_name
FROM products
UNION
SELECT service_name AS item_name
FROM services;

Here, we’re combining products and services into one column, showing all unique items.

⚖️ UNION vs UNION ALL

Feature	UNION	UNION ALL
Duplicates	✅ Removes duplicates	❌ Does not remove
Performance	⏳ Slightly slower	🚀 Faster
Use Case	When you need unique results	When you want all results

📘 Recap

• UNION combines results from multiple queries into a single result set
• Removes duplicate rows by default
• UNION ALL includes all rows, even duplicates