Re: [PR] Update code comment for the cases of regularized RANGE frame and add tests for ORDER BY cases with RANGE frame [arrow-datafusion]

["viirya (via GitHub)" <gi...@apache.org>]

viirya commented on code in PR #8410:
URL: https://github.com/apache/arrow-datafusion/pull/8410#discussion_r1413399215


##########
datafusion/expr/src/window_frame.rs:
##########
@@ -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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