Customers Who Never Order SQL Challenge - PostgreSQL Solution

1. Introduction

In this post, we will explore a common SQL query in PostgreSQL: finding customers who have never placed an order. This type of query is often used in business analysis to identify potential untapped customer segments.

Problem

The challenge is to write a PostgreSQL query to identify customers from a customer table who have never made an order from an order table.

Database Table:

Customers Table:

Id	Name
1	Alice
2	Bob

Orders Table:

OrderId	CustomerId
101	1

3. PostgreSQL Solution

SELECT Name
FROM Customers
WHERE Id NOT IN (SELECT CustomerId FROM Orders);

Output:

Name
Bob

Explanation:

1. The query retrieves the names from the Customers table.

2. It uses a subquery within a WHERE clause to exclude those customers who are present in the Orders table.

3. By selecting customers whose Ids are not in the Orders table, it identifies those who have never placed an order.

4. The result is a list of customers with no corresponding order records.