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🔥 Now, Let’s move to the next topic:

✅ Recursive CTEs

One of the most advanced and impressive SQL topics for interviews 💯

🧠 1. What is a Recursive CTE?

A Recursive CTE is a CTE that refers to itself.

👉 Used for hierarchical or recursive data

Examples:

✔ Employee-Manager hierarchy

✔ Organization chart

✔ Folder structure

✔ Category trees

⚡ 2. Structure of Recursive CTE

A Recursive CTE has two parts:

1️⃣ Anchor Query

Starting point

2️⃣ Recursive Query

Repeats until condition is met

🔥 3. Basic Example – Generate Numbers 1 to 5

WITH RECURSIVE Numbers AS (
    SELECT 1 AS num
    UNION ALL
    SELECT num + 1
    FROM Numbers
    WHERE num < 5
)

SELECT * FROM Numbers;

WITH RECURSIVE EmployeeHierarchy AS (
    SELECT
        emp_id,
        name,
        manager_id,
        1 AS level
    FROM employees
    WHERE manager_id IS NULL
    UNION ALL
    SELECT
        e.emp_id,
        e.name,
        e.manager_id,
        eh.level + 1
    FROM employees e
    JOIN EmployeeHierarchy eh
        ON e.manager_id = eh.emp_id
)

SELECT * FROM EmployeeHierarchy;

🎯 5. Real-World Uses

Organizational Charts

CEO → Manager → Employee

Product Categories

Electronics → Laptop → Gaming Laptop

Folder Structures

Root → Folder → Subfolder

⚡ 6. Important Rule

Every recursive CTE needs:

✔ Anchor Query

✔ Recursive Query

✔ Stopping Condition

Without stopping condition ❌ Infinite loop

🎯 7. Practice Tasks

1. Generate numbers 1–10

2. Generate even numbers

3. Build employee hierarchy

4. Find reporting levels

5. Create category tree

⚡ Mini Challenge 🔥

👉 Generate multiplication table of 5 (5 to 50) using Recursive CTE

Example:

5

10

15

20

...

50

Most asked question:

👉 Difference between CTE and Recursive CTE?

✅ CTE = Temporary result set

✅ Recursive CTE = Temporary result set that references itself

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