Update inactive customer query

src/data/courses/sql-mastery/chapters/multi-table-queries/lessons/inactive-customers.md

@@ -39,11 +39,9 @@ setup: |
   ```
 ---
 
-Given the following data in `customer` and `sale` tables, we need to find the customers who have never placed an order.
+The bookstore's marketing team wants to run a special promotion targeting customers who haven't made any purchases yet. They believe these potential customers might need a little extra encouragement to make their first purchase. Your task is to help identify these inactive customers from the database.
 
-We have the `customer` and `sale` tables.
-
-> `customer` table has the list of customers.
+Given the following data in table `customer`
 
 | id  | name          | email                     |
 | --- | ------------- | ------------------------- |
@@ -54,7 +52,7 @@ We have the `customer` and `sale` tables.
 | 5   | Charlie Davis | charlie.davis@example.com |
 | 6   | David Lee     | david.lee@example.com     |
 
-> `sale` table has the list of sales.
+And the following data in table `sale`
 
 | id  | customer_id | order_date | total_amount |
 | --- | ----------- | ---------- | ------------ |
@@ -66,7 +64,7 @@ We have the `customer` and `sale` tables.
 | 6   | 2           | 2024-11-23 | 300.00       |
 | 7   | 2           | 2024-11-11 | 300.00       |
 
-Write a query to find customers who have never placed an order.
+Write a query to identify all customers who have never placed an order. These are the customers the marketing team wants to target with their special promotion.
 
 ## Expected Output
 
@@ -84,3 +82,25 @@ LEFT JOIN sale s
   ON c.id = s.customer_id
 WHERE s.id IS NULL;
 ```
+
+### Explanation
+
+We start with the `customer` table as we want to keep all customers regardless of whether they have made a purchase:
+
+```sql
+FROM customer c
+```
+
+We use a `LEFT JOIN` with the `sale` table to include all customers and their sales (if any):
+
+```sql
+LEFT JOIN sale s ON c.id = s.customer_id
+```
+
+The `WHERE` clause filters for customers who have no matching records in the `sale` table:
+
+```sql
+WHERE s.id IS NULL
+```
+
+This query efficiently identifies customers who haven't made any purchases yet. The LEFT JOIN ensures we keep all customers from the customer table, while the `WHERE` clause filters out those who have made purchases.