You want to find the average sales amount per customer but only for customers with more than 5 sales. Which query correctly achieves this?

hard📝 Application Q8 of 15

PostgreSQL - Aggregate Functions and GROUP BY

ASELECT customer_id, AVG(amount) FROM sales GROUP BY customer_id HAVING COUNT(*) > 5;

BSELECT customer_id, AVG(amount) FROM sales WHERE COUNT(*) > 5 GROUP BY customer_id;

CSELECT customer_id, AVG(amount) FROM sales GROUP BY customer_id WHERE COUNT(*) > 5;

DSELECT customer_id, AVG(amount) FROM sales HAVING COUNT(*) > 5;

Step-by-Step Solution

Solution:

Step 1: Use GROUP BY to group sales by customer
Grouping by customer_id allows aggregation per customer.
Step 2: Filter groups with HAVING clause
HAVING filters groups after aggregation; COUNT(*) > 5 keeps customers with more than 5 sales.
Final Answer:
SELECT customer_id, AVG(amount) FROM sales GROUP BY customer_id HAVING COUNT(*) > 5; -> Option A
Quick Check:
Use HAVING to filter groups after aggregation [OK]

Quick Trick: Use HAVING to filter aggregated groups, not WHERE [OK]

Common Mistakes:

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