viirya commented on code in PR #8410:
URL: https://github.com/apache/arrow-datafusion/pull/8410#discussion_r1413399215
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datafusion/expr/src/window_frame.rs:
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@@ -148,18 +148,20 @@ impl WindowFrame {
pub fn regularize(mut frame: WindowFrame, order_bys: usize) ->
Result<WindowFrame> {
if frame.units == WindowFrameUnits::Range && order_bys != 1 {
// Normally, RANGE frames require an ORDER BY clause with exactly one
- // column. However, an ORDER BY clause may be absent in two edge cases.
+ // column. However, an ORDER BY clause may be absent in two edge cases:
+ // 1. start bound is UNBOUNDED or CURRENT ROW
+ // 2. end bound is CURRENT ROW or UNBOUNDED.
+ // In these cases, we regularize the RANGE frame to be equivalent to a
ROWS
+ // frame with the UNBOUNDED bounds.
Review Comment:
In short, DataFusion currently allows various `ORDER BY` clause cases
(empty, 1 or more column) with RANGE frame, similar to Postgres.
But for empty `ORDER BY` clause case, the window function result is
different to Postgres.
See added tests.
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