[Solved] Given the tables orders(order_id, customer_id, amount) and customers(customer_id, name), what does this query return?SELECT c.name FROM customers c WHERE EXISTS (SELECT 1 FROM orders o WHERE o.... | PostgreSQL

PostgreSQL - Subqueries in PostgreSQL

Given the tables orders(order_id, customer_id, amount) and customers(customer_id, name), what does this query return?

SELECT c.name FROM customers c WHERE EXISTS (SELECT 1 FROM orders o WHERE o.customer_id = c.customer_id AND o.amount > 100);

ANames of customers with no orders over 100.

BNames of all customers regardless of orders.

CAn error due to missing GROUP BY clause.

DNames of customers who have at least one order with amount over 100.

Step-by-Step Solution

Solution:

Step 1: Understand the EXISTS correlated subquery
The subquery checks if any order for customer has amount > 100.
Step 2: Determine the outer query result
Only customers with such orders are returned.
Final Answer:
Names of customers who have at least one order with amount over 100. -> Option D
Quick Check:
EXISTS filters customers with qualifying orders = Names of customers who have at least one order with amount over 100. [OK]

Quick Trick: EXISTS returns true if subquery finds any matching row. [OK]

Common Mistakes:

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Given the tables orders(order_id, customer_id, amount) and customers(customer_id, name), what does this query return?