How can you calculate the percentage contribution of each sale amount to the total sales per region using window functions?

hard📝 Application Q9 of 15

PostgreSQL - Window Functions in PostgreSQL

ASELECT region, amount, amount * 100.0 / SUM(amount) OVER (PARTITION BY region) AS pct FROM sales

BSELECT region, amount, amount / SUM(amount) FROM sales GROUP BY region

CSELECT region, amount, RANK() OVER (PARTITION BY region ORDER BY amount) AS pct FROM sales

DSELECT region, amount, amount * 100 / COUNT(*) OVER (PARTITION BY region) AS pct FROM sales

Step-by-Step Solution

Solution:

Step 1: Calculate total sales per region using window SUM()
SUM(amount) OVER (PARTITION BY region) computes total sales for each region without grouping rows.
Step 2: Compute percentage contribution
Divide each amount by total sales per region and multiply by 100 for percentage.
Final Answer:
SELECT region, amount, amount * 100.0 / SUM(amount) OVER (PARTITION BY region) AS pct FROM sales -> Option A
Quick Check:
Use window SUM() for totals, then calculate percentage [OK]

Quick Trick: Use SUM() OVER PARTITION for totals, then compute percentage [OK]

Common Mistakes:

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