SQL
Finding Records Without Related Entries
Efficiently identify records in one table that do not have corresponding entries in a related table using a LEFT JOIN and WHERE IS NULL condition.
SELECT c.customer_id, c.customer_name
FROM customers c
LEFT JOIN orders o ON c.customer_id = o.customer_id
WHERE o.order_id IS NULL;
How it works: This SQL query finds all customers who have not placed any orders. It performs a `LEFT JOIN` from the `customers` table to the `orders` table. If a customer has no matching orders, the columns from the `orders` table will be `NULL`. The `WHERE o.order_id IS NULL` condition then filters for these customers, making it easy to identify orphaned or unrelated records.