✅ 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

👨‍💼 employees_2025

Name

- Ajit

- Neha

👨‍💼 employees_2026

name

- Sujit

- Neha

🔥 3. UNION Example

SELECT name FROM employees_2025

UNION

SELECT name FROM employees_2025;

✔️ Removes duplicates automatically

✅ Result

name

- Ajit

- Neha

- Sujit

⚡ 4. UNION ALL

SELECT name FROM employees_2025

UNION ALL

SELECT name FROM employees_2026;

Keeps duplicates
Faster than UNION

✅ Result

name

- Ajit

- Neha

- Sujit

- 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_2025

UNION

SELECT name FROM employees_2026

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

🧠 Why UNION ALL?

👉 UNION → removes duplicates

👉 UNION ALL → keeps duplicates + faster

#union #union_alll

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