[Solved] What will this query return?SELECT id FROM Customers c WHERE NOT EXISTS (SELECT 1 FROM Orders o WHERE o.customer_id = c.id);Tables: Customers(id), Orders(id, customer_id) | SQL

SQL - Subqueries

What will this query return?

SELECT id FROM Customers c WHERE NOT EXISTS (SELECT 1 FROM Orders o WHERE o.customer_id = c.id);

Tables: Customers(id), Orders(id, customer_id)

AIDs of orders without customers

BIDs of customers with at least one order

CAll customer IDs

DIDs of customers with no orders

Step-by-Step Solution

Solution:

Step 1: Analyze NOT EXISTS condition
The subquery checks for orders linked to each customer. NOT EXISTS means no matching orders found.
Step 2: Determine returned rows
The query returns customer IDs where no orders exist.
Final Answer:
IDs of customers with no orders -> Option D
Quick Check:
NOT EXISTS finds customers without orders [OK]

Quick Trick: NOT EXISTS finds rows with no matching subquery rows [OK]

Common Mistakes:

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