[Solved] Given tables orders(order_id, customer_id) and customers(customer_id, name), which query lists all customers including those without any orders? | PostgreSQL

PostgreSQL - Joins in PostgreSQL

Given tables orders(order_id, customer_id) and customers(customer_id, name), which query lists all customers including those without any orders?

ASELECT customers.name, orders.order_id FROM customers RIGHT JOIN orders ON customers.customer_id = orders.customer_id;

BSELECT customers.name, orders.order_id FROM orders LEFT JOIN customers ON orders.customer_id = customers.customer_id;

CSELECT customers.name, orders.order_id FROM customers INNER JOIN orders ON customers.customer_id = orders.customer_id;

DSELECT customers.name, orders.order_id FROM customers LEFT JOIN orders ON customers.customer_id = orders.customer_id;

Step-by-Step Solution

Solution:

Step 1: Understand requirement
List all customers, including those without orders.
Step 2: Choose correct JOIN type
LEFT JOIN with customers as left table includes all customers.
Step 3: Evaluate options
SELECT customers.name, orders.order_id FROM customers LEFT JOIN orders ON customers.customer_id = orders.customer_id; correctly uses LEFT JOIN from customers to orders. SELECT customers.name, orders.order_id FROM orders LEFT JOIN customers ON orders.customer_id = customers.customer_id; reverses tables, excluding customers without orders. SELECT customers.name, orders.order_id FROM customers INNER JOIN orders ON customers.customer_id = orders.customer_id; uses INNER JOIN, excluding customers without orders. SELECT customers.name, orders.order_id FROM customers RIGHT JOIN orders ON customers.customer_id = orders.customer_id; uses RIGHT JOIN but with reversed tables, not meeting requirement.
Final Answer:
SELECT customers.name, orders.order_id FROM customers LEFT JOIN orders ON customers.customer_id = orders.customer_id; -> Option D
Quick Check:
LEFT JOIN keeps all rows from left table [OK]

Quick Trick: Use LEFT JOIN with main table on left [OK]

Common Mistakes:

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Given tables orders(order_id, customer_id) and customers(customer_id, name), which query lists all customers including those without any orders?