Solution:Step 1: Use LEFT JOIN to keep all ordersLEFT JOIN keeps all orders even if no matching customer exists.Step 2: Replace NULL customer names with 'Unknown'Use COALESCE to show 'Unknown' when c.name is NULL.Final Answer:SELECT o.order_id, COALESCE(c.name, 'Unknown') AS customer_name FROM Order

[Solved] You have two tables:Orders:order_id | customer_id1 | 1012 | 1023 | 103Customers:customer_id | name101 | John102 | JaneYou want to list all orders with customer names, but show 'Unknown' if no... | SQL

SQL - LEFT and RIGHT JOIN

ASELECT o.order_id, COALESCE(c.name, 'Unknown') AS customer_name FROM Orders o LEFT JOIN Customers c ON o.customer_id = c.customer_id;

BSELECT o.order_id, IFNULL(c.name, 'Unknown') AS customer_name FROM Orders o INNER JOIN Customers c ON o.customer_id = c.customer_id;

CSELECT o.order_id, c.name FROM Orders o RIGHT JOIN Customers c ON o.customer_id = c.customer_id;

DSELECT o.order_id, CASE WHEN c.name IS NULL THEN 'Unknown' ELSE c.name END FROM Orders o JOIN Customers c ON o.customer_id = c.customer_id;

Step-by-Step Solution

Solution:

Step 1: Use LEFT JOIN to keep all orders
LEFT JOIN keeps all orders even if no matching customer exists.
Step 2: Replace NULL customer names with 'Unknown'
Use COALESCE to show 'Unknown' when c.name is NULL.
Final Answer:
SELECT o.order_id, COALESCE(c.name, 'Unknown') AS customer_name FROM Orders o LEFT JOIN Customers c ON o.customer_id = c.customer_id; -> Option A
Quick Check:
LEFT JOIN + COALESCE handles missing customers [OK]

Quick Trick: Use LEFT JOIN with COALESCE to replace NULLs [OK]

Common Mistakes:

MISTAKES

Using INNER JOIN excludes orders without customers
Using RIGHT JOIN reverses table roles incorrectly
Forgetting to handle NULL customer names

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More SQL Quizzes

You have two tables:

Step 1: Use LEFT JOIN to keep all orders

Step 2: Replace NULL customer names with 'Unknown'

Final Answer:

Quick Check:

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