[Solved] Which of the following best describes how PARTITION BY affects window function results? — Ans: It resets the window function calculation for each partition group | PostgreSQL

PostgreSQL - Window Functions in PostgreSQL

Which of the following best describes how PARTITION BY affects window function results?

AIt applies the window function only once to the entire table

BIt resets the window function calculation for each partition group

CIt removes duplicate rows from the result set

DIt changes the data type of the window function output

Step-by-Step Solution

Solution:

Step 1: Understand window function behavior with PARTITION BY
PARTITION BY divides rows into groups; window functions restart calculation for each group.
Step 2: Eliminate incorrect options
Window functions always run per row; PARTITION BY does not remove duplicates or change data types.
Final Answer:
It resets the window function calculation for each partition group -> Option B
Quick Check:
PARTITION BY resets window function per group = true [OK]

Quick Trick: Window functions restart per PARTITION BY group, not once globally [OK]

Common Mistakes:

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Which of the following best describes how PARTITION BY affects window function results?