Find Customer Referee

LeetCode 584 | Difficulty: Easy

Easy

Problem Description

Table: Customer

+-------------+---------+
| Column Name | Type    |
+-------------+---------+
| id          | int     |
| name        | varchar |
| referee_id  | int     |
+-------------+---------+
In SQL, id is the primary key column for this table.
Each row of this table indicates the id of a customer, their name, and the id of the customer who referred them.

Find the names of the customer that are either:

- **referred by** any customer with `id != 2`.

- **not referred by** any customer.

Return the result table in any order.

The result format is in the following example.

Example 1:

Input: 
Customer table:
+----+------+------------+
| id | name | referee_id |
+----+------+------------+
| 1  | Will | null       |
| 2  | Jane | null       |
| 3  | Alex | 2          |
| 4  | Bill | null       |
| 5  | Zack | 1          |
| 6  | Mark | 2          |
+----+------+------------+
Output: 
+------+
| name |
+------+
| Will |
| Jane |
| Bill |
| Zack |
+------+

Topics: Database

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Approach

Direct Approach

This problem can typically be solved with straightforward iteration or simple data structure usage. Focus on correctness first, then optimize.

When to use

Basic problems that test fundamental programming skills.

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Solutions

Solution 1: MySQL (Best: 1275 ms)

Metric	Value
Runtime	1275 ms
Memory	N/A
Date	2018-05-08

Solution

# Write your MySQL query statement below
select name from customer where referee_id <> 2 OR referee_id is null

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Complexity Analysis

Approach	Time	Space
Solution	$O(n)$	$O(1) to O(n)$

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Interview Tips

Key Points

• Start by clarifying edge cases: empty input, single element, all duplicates.
• LeetCode provides 1 hint(s) for this problem — try solving without them first.

💡 Hints

Hint 1: Be careful of the NULL value