[Solved] What does the SQL clause ROWS BETWEEN 2 PRECEDING AND CURRENT ROW do in a window function? — Ans: It calculates the function over the current row and the two rows before it. | SQL

SQL - Advanced Window Functions

What does the SQL clause ROWS BETWEEN 2 PRECEDING AND CURRENT ROW do in a window function?

AIt calculates the function over the current row and the two rows before it.

BIt calculates the function over the current row and the next two rows.

CIt calculates the function over all rows in the table.

DIt calculates the function only on the current row.

Step-by-Step Solution

Solution:

Step 1: Understand the window frame boundaries
The clause ROWS BETWEEN 2 PRECEDING AND CURRENT ROW means the frame includes the current row and the two rows before it.
Step 2: Apply to window function calculation
The window function (like AVG) will compute its result using values from these three rows.
Final Answer:
It calculates the function over the current row and the two rows before it. -> Option A
Quick Check:
Window frame includes current + 2 preceding rows = C [OK]

Quick Trick: Preceding means rows before current, including current [OK]

Common Mistakes:

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What does the SQL clause ROWS BETWEEN 2 PRECEDING AND CURRENT ROW do in a window function?