[Solved] You have two tables: Customers and Orders. Some customers have no orders. You want a list of all customers with their order counts, showing zero for customers without orders.... | SQL

SQL - LEFT and RIGHT JOIN

You have two tables: Customers and Orders. Some customers have no orders. You want a list of all customers with their order counts, showing zero for customers without orders. Which query achieves this?

ASELECT Customers.name, COUNT(Orders.id) FROM Customers LEFT OUTER JOIN Orders ON Customers.id = Orders.customer_id GROUP BY Customers.name;

BSELECT Customers.name, COUNT(Orders.id) FROM Customers INNER JOIN Orders ON Customers.id = Orders.customer_id GROUP BY Customers.name;

CSELECT Customers.name, COUNT(Orders.id) FROM Orders LEFT OUTER JOIN Customers ON Customers.id = Orders.customer_id GROUP BY Customers.name;

DSELECT Customers.name, COUNT(*) FROM Customers RIGHT OUTER JOIN Orders ON Customers.id = Orders.customer_id GROUP BY Customers.name;

Step-by-Step Solution

Solution:

Step 1: Identify join type needed
LEFT OUTER JOIN keeps all customers, including those without orders.
Step 2: Use COUNT on Orders.id
COUNT(Orders.id) counts orders per customer; zero if no orders due to NULLs.
Final Answer:
SELECT Customers.name, COUNT(Orders.id) FROM Customers LEFT OUTER JOIN Orders ON Customers.id = Orders.customer_id GROUP BY Customers.name; -> Option A
Quick Check:
LEFT OUTER JOIN + COUNT(Orders.id) = zero for no orders [OK]

Quick Trick: Use LEFT OUTER JOIN and COUNT(column) for zero counts [OK]

Common Mistakes:

MISTAKES

Using INNER JOIN excludes customers without orders
Counting * instead of column causes wrong counts
Reversing join order changes results

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Which query achieves this?

Step 1: Identify join type needed

Step 2: Use COUNT on Orders.id

Final Answer:

Quick Check:

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