LeetCode SQL - Subquery

Table of contents

Subquery

183. Customers Who Never Order

SELECT c."name" AS "Customers"
FROM Customers c
WHERE
    NOT EXISTS (
        SELECT DISTINCT customerId
        FROM Orders o
        WHERE c.id = o.customerId
    )

608. Tree Node

SELECT
    id,
    CASE
        WHEN p_id IS NULL THEN 'Root'
        WHEN id IN (SELECT p_id FROM tree) THEN 'Inner'
        ELSE 'Leaf'
    END AS "type"
FROM
    tree