What is a window frame?

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Accepted Answer

A window frame narrows the calculation further inside each partition. The default frame for ORDER BY is ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW, meaning the function accumulates from the start of the partition up to the current row. You can override this - for example ROWS BETWEEN 2 PRECEDING AND CURRENT ROW limits the frame to the current row plus the two rows before it, which is how a 3-row moving average works. Functions like ROW_NUMBER and RANK ignore the frame entirely; functions like SUM and AVG respect it.