[Solved] What does the PARTITION BY clause do in a window function in PostgreSQL? — Ans: It divides the rows into groups to perform calculations within each group. | PostgreSQL

PostgreSQL - Window Functions in PostgreSQL

What does the PARTITION BY clause do in a window function in PostgreSQL?

AIt filters rows before the window function is applied.

BIt divides the rows into groups to perform calculations within each group.

CIt sorts the entire table before applying the window function.

DIt removes duplicate rows from the result set.

Step-by-Step Solution

Solution:

Step 1: Understand the role of PARTITION BY
PARTITION BY groups rows so window functions calculate results within each group separately.
Step 2: Differentiate from filtering and sorting
Filtering removes rows, sorting orders rows, but PARTITION BY only groups rows without removing or sorting them globally.
Final Answer:
It divides the rows into groups to perform calculations within each group. -> Option B
Quick Check:
PARTITION BY = grouping rows for window functions [OK]

Quick Trick: Remember: PARTITION BY groups rows, it does not filter or sort [OK]

Common Mistakes:

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What does the PARTITION BY clause do in a window function in PostgreSQL?