Date: January 29, 2026
Category: SQL
Time Taken: 10 minute
Difficulty: Easy

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Problem Statement

Write a solution to find the names of all the salespersons who did not have any orders related to the company with the name "RED".

Link: Sales Person

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Approach 1 (CTE):

• First, we can create a CTE to store all orders where the company name is "RED".

• Then, we will perform a Left Join between SalesPerson and the CTE using their sales_id.

• The Left Join ensures that any sales_id in the CTE that doesn't match a SalesPerson sales_id will be null. We will use a filter condition to select the names where the CTE sales_id is NULL.

Solution Code:

WITH red_orders AS (
    SELECT o.sales_id
    FROM Orders o
    JOIN Company c ON o.com_id = c.com_id
    WHERE c.name = 'RED'
)

SELECT s.name
FROM SalesPerson s
LEFT JOIN red_orders r ON s.sales_id = r.sales_id
WHERE r.sales_id IS NULL

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Approach 2 (NOT EXISTS):

Solution Code:

• In this approach, we will use the NOT EXISTS clause to select all values that don't meet the condition.

• In the condition, we will select companies with the name "RED" and match them with the SalesPerson sales_id.

• This will return the name from SalesPerson for whom the sales_id does not exist.

SELECT s.name
FROM SalesPerson AS s
WHERE NOT EXISTS (
    SELECT 1
    FROM Orders AS o
    JOIN Company AS c
    ON o.com_id = c.com_id
    WHERE c.name = "RED" AND s.sales_id = o.sales_id
)

Key Takeaway: How to use NOT EXISTS properly, still unsure but got better understanding.

Pattern: Aggregation

Mistakes I Made: Many, was not able to solve without help.

Series: 90 Days of Data Engineering Progress: 26/90 problems completed

Tags: #DEQuest #LeetCode #SQL #DataEngineering #BuildInPublic