[Solved] How can subqueries help when you need to delete all customers who have no orders? — Ans: DELETE FROM customers WHERE id NOT IN (SELECT customer_id FROM orders) | SQL

SQL - Subqueries

How can subqueries help when you need to delete all customers who have no orders?

ADELETE FROM customers WHERE id IN (SELECT customer_id FROM orders)

BDELETE FROM customers WHERE id NOT IN (SELECT customer_id FROM orders)

CDELETE FROM customers WHERE EXISTS (SELECT * FROM orders)

DDELETE FROM customers WHERE id = (SELECT customer_id FROM orders)

Step-by-Step Solution

Solution:

Step 1: Understand the goal
We want to delete customers who do not appear in the orders table.
Step 2: Analyze options
DELETE FROM customers WHERE id NOT IN (SELECT customer_id FROM orders) deletes customers whose id is not in the list of customer_ids from orders, correctly identifying those with no orders.
Final Answer:
DELETE FROM customers WHERE id NOT IN (SELECT customer_id FROM orders) -> Option B
Quick Check:
Subquery finds customers with orders, NOT IN deletes those without [OK]

Quick Trick: Use NOT IN with subqueries to find missing related rows [OK]

Common Mistakes:

MISTAKES

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How can subqueries help when you need to delete all customers who have no orders?