window_funcs Expression Audits#

Audit notes for expressions in this category that have been audited. Absence of an entry means the expression has not been audited yet, not that it is unsupported. See the user guide Spark Expression Support for current support status.

avg (window)#

  • 4.1.1, audited 2026-06-25: AVG(<decimal>) over a window runs natively on Spark 4.x. Spark wraps the result as Cast(avg(UnscaledValue(v)) / pow10 as decimal); CometWindowExec.convert unwraps that shape alongside Alias(WindowExpression) and Alias(MakeDecimal(WindowExpression)), so the AvgDecimal native window branch in process_agg_func is reachable. Non-decimal AVG runs natively. Sliding-frame decimal AVG is guarded by the same fallback as decimal SUM (see below) so that it cannot hit the DataFusion built-in overflow divergence.

lag#

  • Supported via CometWindowExec (operator level), not the expression serde.

lead#

  • Supported via CometWindowExec (operator level), not the expression serde.

sum (window)#

  • 4.1.1, audited 2026-06-25: SUM(<decimal>) over a sliding window frame (lower bound not UNBOUNDED PRECEDING) falls back to Spark. The native sliding path would use DataFusion’s built-in sum, which wraps on overflow rather than returning Spark’s NULL, and overflow cannot be detected at plan time, so the whole sliding decimal SUM case falls back. Ever-expanding frames use Comet’s overflow-aware SumDecimal UDAF and run natively, matching Spark including overflow-to-NULL. Bigint sliding SUM overflow matches Spark (both wrap) and stays native.