Given the table transactions(tx_date, value) ordered by tx_date, what does this query return?

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PostgreSQL - Window Functions in PostgreSQL

Given the table transactions(tx_date, value) ordered by tx_date, what does this query return?

SELECT tx_date, value, AVG(value) OVER (ORDER BY tx_date RANGE BETWEEN INTERVAL '2 days' PRECEDING AND CURRENT ROW) AS avg_2days FROM transactions;

AThe average of values from all rows with <code>tx_date</code> within 2 days before and including the current row's date

BThe average of values from the 2 rows preceding the current row and the current row

CThe average of values from all rows in the partition

DThe average of values from the current row only

Step-by-Step Solution

Solution:

Step 1: Understand RANGE BETWEEN with INTERVAL
The RANGE BETWEEN INTERVAL '2 days' PRECEDING AND CURRENT ROW includes all rows where tx_date is within 2 days before up to the current row's tx_date.
Step 2: Differentiate from ROWS
This is based on logical value ranges, not physical row counts.
Final Answer:
The average of values from all rows with tx_date within 2 days before and including the current row's date -> Option A
Quick Check:
RANGE uses value intervals, not row counts [OK]

Quick Trick: RANGE with INTERVAL filters by value range, not row count [OK]

Common Mistakes:

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