0 of 50 solved/50

584. Find Customer Referee

SQL 50 · Select (day 1). Decode it with the hints, solve it on LeetCode, then compare with the reference solution in MySQLPostgreSQL.

Your work

Status Notes Your solution (MySQLPostgreSQL)

Open one at a time. Try to finish with as few as you can.

1. What does one output row represent?

One customer.

2. Approach

WHERE referee_id <> 2 OR referee_id IS NULL.

3. The trap

NULL <> 2 is unknown, not true. Customers with no referee vanish without the IS NULL.

Tested on MySQL 8.0 and PostgreSQL 16. Switch dialect at the top of the page.

Show the MySQLPostgreSQL solution

SELECT name
FROM Customer
WHERE referee_id <> 2 OR referee_id IS NULL;

Note: PostgreSQL also has WHERE referee_id IS DISTINCT FROM 2, which treats NULL as a normal value.