[Solved] Find the mistake in this query to get unmatched orders:SELECT o.order_id FROM orders o LEFT JOIN customers c ON o.customer_id = c.id WHERE c.id IS NOT NULL; | SQL

SQL - LEFT and RIGHT JOIN

Find the mistake in this query to get unmatched orders:

SELECT o.order_id FROM orders o LEFT JOIN customers c ON o.customer_id = c.id WHERE c.id IS NOT NULL;

AThe JOIN should be RIGHT JOIN

BThe ON condition is reversed

CThe WHERE clause should check c.id IS NULL to find unmatched orders

DNo mistake, query is correct

Step-by-Step Solution

Solution:

Step 1: LEFT JOIN keeps all orders
Orders matched with customers or NULL if no match.
Step 2: Filter unmatched orders
WHERE c.id IS NOT NULL filters matched orders; to find unmatched, use c.id IS NULL.
Final Answer:
The WHERE clause should check c.id IS NULL to find unmatched orders -> Option C
Quick Check:
Use NULL check on right table to find unmatched [OK]

Quick Trick: Use WHERE right_table.key IS NULL to find unmatched rows [OK]

Common Mistakes:

MISTAKES

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