You want to find the total sales quantity for each product in each region from the sales table with columns product_id, region, and quantity. Which query correctly groups and sums the data?

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PostgreSQL - Aggregate Functions and GROUP BY

You want to find the total sales quantity for each product in each region from the sales table with columns product_id, region, and quantity. Which query correctly groups and sums the data?

ASELECT product_id, SUM(quantity) FROM sales GROUP BY product_id;

BSELECT product_id, region, SUM(quantity) FROM sales GROUP BY product_id;

CSELECT product_id, region, SUM(quantity) FROM sales GROUP BY product_id, region;

DSELECT product_id, region, SUM(quantity) FROM sales;

Step-by-Step Solution

Solution:

Step 1: Identify grouping needs
We want totals per product and per region, so both columns must be grouped.
Step 2: Check each option's GROUP BY clause
SELECT product_id, region, SUM(quantity) FROM sales GROUP BY product_id, region; groups by product_id and region, matching SELECT columns; others miss region or GROUP BY entirely.
Final Answer:
SELECT product_id, region, SUM(quantity) FROM sales GROUP BY product_id, region; -> Option C
Quick Check:
Group by all non-aggregated columns for correct totals [OK]

Quick Trick: Group by all selected non-aggregated columns [OK]

Common Mistakes:

Grouping by only one column when selecting multiple
Omitting GROUP BY causing aggregation errors
Selecting columns without aggregation or grouping

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You want to find the total sales quantity for each product in each region from the sales table with columns product_id, region, and quantity. Which query correctly groups and sums the data?

Step 1: Identify grouping needs

Step 2: Check each option's GROUP BY clause

Final Answer:

Quick Check:

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