[Solved] Given the table sales with columns region, product, and amount, what will be the output rows count of this query?SELECT region, product, SUM(amount) FROM sales GROUP BY ROLLUP(region, product); | PostgreSQL

PostgreSQL - Aggregate Functions and GROUP BY

Given the table sales with columns region, product, and amount, what will be the output rows count of this query?

SELECT region, product, SUM(amount) FROM sales GROUP BY ROLLUP(region, product);

ANumber of distinct (region, product) pairs plus one subtotal per region plus one grand total row.

BNumber of distinct (region, product) pairs only.

CNumber of distinct regions only.

DNumber of distinct products only.

Step-by-Step Solution

Solution:

Step 1: Understand ROLLUP output rows
ROLLUP(region, product) returns all (region, product) groups, plus subtotals per region, plus a grand total row.
Step 2: Count rows
Total rows = distinct (region, product) + distinct regions (subtotals) + 1 (grand total).
Final Answer:
Number of distinct (region, product) pairs plus one subtotal per region plus one grand total row. -> Option A
Quick Check:
ROLLUP adds subtotals and grand total [OK]

Quick Trick: ROLLUP adds subtotals and grand total rows [OK]

Common Mistakes:

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Given the table sales with columns region, product, and amount, what will be the output rows count of this query?