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Update code comment for the cases of regularized RANGE frame and add tests for ORDER BY cases with RANGE frame #8410

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Dec 4, 2023
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Update code comment for the cases of regularized RANGE frame and add tests for ORDER BY cases with RANGE frame #8410

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86871a8
fix: RANGE frame can be regularized to ROWS frame only if empty ORDER…
viirya Dec 3, 2023
ab0b486
Fix flaky test
viirya Dec 3, 2023
f12b9e6
Update test comment
viirya Dec 4, 2023
6926b2f
Add code comment
viirya Dec 4, 2023
f22a1ca
Update
viirya Dec 4, 2023
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12 changes: 11 additions & 1 deletion datafusion/expr/src/window_frame.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -148,12 +148,22 @@ 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 or present but with
// more than one column 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.
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Note that actually Spark doesn't allow empty ORDER BY clause for RANGE frame in any cases. I updated this according to the comment.

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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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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 order by a RANGE between 1 PRECEDING AND 2 FOLLOWING) rnk from (select 1 a) q;
 a | rnk 
---+-----
 1 |   1
(1 row)

postgres=# select a, rank() over (partition by a order by a, a + 1 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 order by a, a + 1 RANG...

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Hmm, actually Postgres behavior allows empty ORDER BY clause, one column or multiple column ORDER BY clause with RANGE frame if start bound/end bound is UNBOUNDED or CURRENT ROW.

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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.

// Note that this follows Postgres behavior.
if (frame.start_bound.is_unbounded()
|| frame.start_bound == WindowFrameBound::CurrentRow)
&& (frame.end_bound == WindowFrameBound::CurrentRow
|| frame.end_bound.is_unbounded())
{
// If an ORDER BY clause is absent, the frame is equivalent to a ROWS
// frame with the UNBOUNDED bounds.
// If an ORDER BY clause is present but has more than one column, the
// frame is unchanged.
Comment on lines +163 to +166
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@viirya viirya Dec 4, 2023 •
edited
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Actually, based on Postgres behavior, it doesn't change the RANGE frame to ROWS frame (see the added tests in sqllogictest which return different results than Postgres).

Based on Postgres doc, without ORDER BY, Postgres treats all rows of the partition as peers of the current row (https://www.postgresql.org/docs/current/sql-expressions.html#SYNTAX-WINDOW-FUNCTIONS).

if order_bys == 0 {
frame.units = WindowFrameUnits::Rows;
frame.start_bound =
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58 changes: 58 additions & 0 deletions datafusion/sqllogictest/test_files/window.slt
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Expand Up @@ -3727,3 +3727,61 @@ FROM score_board s

statement ok
DROP TABLE score_board;

# Regularize RANGE frame
query error DataFusion error: Error during planning: RANGE requires exactly one ORDER BY column
select a,
rank() over (order by a, a + 1 RANGE BETWEEN UNBOUNDED PRECEDING AND 1 FOLLOWING) rnk
from (select 1 a union select 2 a) q ORDER BY a

query II
select a,
rank() over (order by a RANGE BETWEEN UNBOUNDED PRECEDING AND 1 FOLLOWING) rnk
from (select 1 a union select 2 a) q ORDER BY a
----
1 1
2 2

query error DataFusion error: Error during planning: RANGE requires exactly one ORDER BY column
select a,
rank() over (RANGE BETWEEN UNBOUNDED PRECEDING AND 1 FOLLOWING) rnk
from (select 1 a union select 2 a) q ORDER BY a

query II
select a,
rank() over (order by a, a + 1 RANGE BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING) rnk
from (select 1 a union select 2 a) q ORDER BY a
----
1 1
2 2

query II
select a,
rank() over (order by a RANGE BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING) rnk
from (select 1 a union select 2 a) q ORDER BY a
----
1 1
2 2

# TODO: this is different to Postgres which returns [1, 1] for `rnk`.
# Comment it because it is flaky now as it depends on the order of the `a` column.
# query II
# select a,
# rank() over (RANGE BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING) rnk
# from (select 1 a union select 2 a) q ORDER BY rnk
# ----
# 1 1
# 2 2

# TODO: this works in Postgres which returns [1, 1].
query error DataFusion error: Arrow error: Invalid argument error: must either specify a row count or at least one column
select rank() over (RANGE between UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING) rnk
from (select 1 a union select 2 a) q;

# TODO: this is different to Postgres which returns [1, 1] for `rnk`.
query I
select rank() over (order by 1 RANGE BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING) rnk
from (select 1 a union select 2 a) q ORDER BY rnk
----
1
2
Comment on lines +3781 to +3787
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I have a fix for the issue locally. But this PR focuses on doc and test change, so I will submit the fix after this is merged.