🔥 Now, Let’s move to the next topic:

✅ UNION & UNION ALL in SQL

🧠 1. What is UNION?
UNION is used to combine results from multiple SELECT queries.

"Merge data from two tables into one result.”

⚡ 2. Rules for UNION
✔ Same number of columns
✔ Same datatype/order of columns

📊 Example Tables

👨‍💼 employees₂024
name
• Amit
• Neha

👨‍💼 employees₂025
name
• Ravi
• Neha

🔥 3. UNION Example

SELECT name FROM employees_2024
UNION
SELECT name FROM employees_2025;

✔ Removes duplicates automatically

✅ Result
name
• Amit
• Neha
• Ravi

⚡ 4. UNION ALL

SELECT name FROM employees_2024
UNION ALL
SELECT name FROM employees_2025;

✔ Keeps duplicates
✔ Faster than UNION

✅ Result
name
• Amit
• Neha
• Ravi
• Neha

🔥 5. UNION vs UNION ALL

UNION
• Removes duplicates
• Slower
• Doesn't keep all rows

UNION ALL
• Doesn't remove duplicates
• Faster
• Keeps all rows

⚡ 6. ORDER BY with UNION

SELECT name FROM employees_2024
UNION
SELECT name FROM employees_2025
ORDER BY name;

🎯 7. Practice Tasks
1. Combine employee names using UNION
2. Combine employee names using UNION ALL
3. Identify duplicate removal
4. Sort UNION result using ORDER BY
5. Compare UNION vs UNION ALL output

⚡ Mini Challenge 🔥
👉 Combine customer names from two branches and keep duplicates

🔥 Mini Challenge Solution 💯

👉 Since duplicates should remain → use UNION ALL

✅ Example Tables

🏢 branch_a_customers
customer_name
• Amit
• Neha

🏢 branch_b_customers
customer_name
• Ravi
• Neha

✅ SQL Solution

SELECT customer_name
FROM branch_a_customers

UNION ALL

SELECT customer_name
FROM branch_b_customers;

✅ Result
customer_name
• Amit
• Neha
• Ravi
• Neha

✔ Duplicate Neha is preserved 💯

🧠 Why UNION ALL?
👉 UNION → removes duplicates
👉 UNION ALL → keeps duplicates + faster

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