Given the table transactions(customer_id, product_id, total), what will be the result of this query?

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PostgreSQL - Aggregate Functions and GROUP BY

Given the table transactions(customer_id, product_id, total), what will be the result of this query?

SELECT customer_id, product_id, SUM(total) FROM transactions GROUP BY GROUPING SETS ((customer_id), (product_id));

Choose the correct description of the output.

AIt returns total sales grouped by customer_id, product_id, and their combination.

BIt returns total sales grouped by both customer_id and product_id combined only.

CIt returns total sales grouped by customer_id and total sales grouped by product_id separately.

DIt returns total sales without any grouping.

Step-by-Step Solution

Solution:

Step 1: Understand GROUPING SETS behavior
GROUPING SETS ((customer_id), (product_id)) produces two grouping sets: one by customer_id and one by product_id.
Step 2: Analyze output
The query returns sums grouped separately by customer_id and by product_id, not combined.
Final Answer:
It returns total sales grouped by customer_id and total sales grouped by product_id separately. -> Option C
Quick Check:
GROUPING SETS creates multiple grouping sets, not combined unless specified [OK]

Quick Trick: GROUPING SETS lists separate groupings, not combined [OK]

Common Mistakes:

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