[Solved] What will this query return?SELECT id FROM customers WHERE EXISTS (SELECT 1 FROM orders WHERE orders.customer_id = customers.id AND orders.amount > 100); | PostgreSQL

PostgreSQL - Subqueries in PostgreSQL

What will this query return?

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

ACustomer IDs with orders over 100 amount

BCustomer IDs with no orders

CAll customer IDs

DAn error due to missing GROUP BY

Step-by-Step Solution

Solution:

Step 1: Analyze the subquery condition
The subquery looks for orders with amount greater than 100 for each customer.
Step 2: Understand EXISTS effect
EXISTS returns true if such orders exist, so customers with orders over 100 are selected.
Final Answer:
Customer IDs with orders over 100 amount -> Option A
Quick Check:
EXISTS filters customers with large orders = C [OK]

Quick Trick: EXISTS filters rows based on subquery conditions [OK]

Common Mistakes:

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What will this query return?