How do you write a PostgreSQL query to compute a cumulative sum of sales ordered by date using a window function?

easy📝 Syntax Q3 of 15

PostgreSQL - Window Functions in PostgreSQL

ASELECT date, sales, SUM(sales) OVER (ORDER BY date) AS cumulative_sales FROM sales_data;

BSELECT date, sales, SUM(sales) GROUP BY date ORDER BY date;

CSELECT date, sales, SUM(sales) FROM sales_data WINDOW ORDER BY date;

DSELECT date, sales, SUM(sales) PARTITION BY date ORDER BY sales;

Step-by-Step Solution

Solution:

Step 1: Use SUM() as window function
SUM(sales) OVER (ORDER BY date) calculates running total ordered by date.
Step 2: Check syntax correctness
SELECT date, sales, SUM(sales) OVER (ORDER BY date) AS cumulative_sales FROM sales_data; uses correct OVER clause syntax with ORDER BY inside parentheses.
Final Answer:
SELECT date, sales, SUM(sales) OVER (ORDER BY date) AS cumulative_sales FROM sales_data; -> Option A
Quick Check:
SUM() OVER (ORDER BY ...) computes running totals [OK]

Quick Trick: Use SUM() OVER (ORDER BY column) for running totals [OK]

Common Mistakes:

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