Part2 SQL 50 | 584 LeetCode Solved: Find Customer Referee | Complete SQL Query Tutorial

I walk you through solving the SQL problem where we need to find customers who were not referred by the customer with ID = 2.

In this video, I walk you through solving the SQL problem where we need to find customers who were not referred by the customer with ID = 2. Using this LeetCode problem, we will explore how to filter results using `WHERE` conditions, `NOT IN`, and handling `NULL` values in SQL.

We will look at multiple solutions using `!=`, 'angle bracket', and `NOT IN` to achieve the desired result. If you're preparing for SQL technical interviews or simply want to strengthen your SQL skills, this is a must-watch!

🔍 Problem:
We are given a table with customer details, including their referee's ID. Our task is to find the names of the customers who were not referred by the customer with ID = 2.

📝 Solutions Covered:
1. `NOT IN` Clause
2. `!=` and 'angle bracket' Comparison Operators
3. Handling `NULL` Values in SQL Queries

✅ **Solutions**:
```sql
-- Solution 1: Using NOT IN
SELECT name FROM customer WHERE referee_id NOT IN (2) OR referee_id IS NULL;

-- Solution 2: Using != Operator
SELECT name FROM customer WHERE referee_id != 2 OR referee_id IS NULL;

-- Solution 3: Using 'angle bracket' Operator
SELECT name FROM customer WHERE referee_id 'angle bracket' 2 OR referee_id IS NULL;
```

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