viirya commented on code in PR #8410:
URL: https://github.com/apache/arrow-datafusion/pull/8410#discussion_r1413246702
##########
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:
So DataFusion is following Postgres behavior on this.
```
postgres=# select a, rank() over (partition by a RANGE between 1 PRECEDING
AND 2 FOLLOWING) rnk from (select 1 a) q;
ERROR: RANGE with offset PRECEDING/FOLLOWING requires exactly one ORDER BY
column
LINE 1: select a, rank() over (partition by a RANGE between 1 PRECED...
^
postgres=# select a, rank() over (partition by a RANGE between UNBOUNDED
PRECEDING AND UNBOUNDED FOLLOWING) rnk from (select 1 a) q;
a | rnk
---+-----
1 | 1
(1 row)
```
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