mustafasrepo opened a new pull request, #6482:
URL: https://github.com/apache/arrow-datafusion/pull/6482
# Which issue does this PR close?
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Closes #.
# Rationale for this change
Some of the seemingly conflicting ordering requirements can be resolved by
reversing the aggregation function if possible.
For instance, consider query below
```sql
SELECT country, FIRST_VALUE(amount ORDER BY amount ASC) AS fv1,
LAST_VALUE(amount ORDER BY amount DESC) AS fv2,
ARRAY_AGG(amount ORDER BY amount ASC) AS amounts
FROM sales_global
GROUP BY country
```
requirements `amount ASC` by `FIRST_VALUE`, and `amount DESC` by `LAST_VALUE
`are conflicting. However, `FIRST_VALUE(amount ORDER BY amount ASC) AS fv1` is
equivalent to `LAST_VALUE(amount ORDER BY amount DESC) AS fv1`, in terms of
behavior. Hence by converting query above to its equivalent form below
```sql
SELECT country, LAST_VALUE(amount ORDER BY amount DESC) AS fv1,
LAST_VALUE(amount ORDER BY amount DESC) AS fv2,
ARRAY_AGG(amount ORDER BY amount ASC) AS amounts
FROM sales_global
GROUP BY country
```
we can resolve conflicting requirement, and successfully run equivalent
version.
As another use case assume that, `sales_global` table is ordered by `ts
ASC`. Query below,
```sql
SELECT country, LAST_VALUE(amount ORDER BY ts DESC) AS lv1
FROM sales_global
GROUP BY country
```
It produces following plan
```sql
ProjectionExec: expr=[country@0 as country, LAST_VALUE(sales_global.amount)
ORDER BY [sales_global.ts DESC NULLS FIRST]@1 as lv1]
AggregateExec: mode=Single, gby=[country@0 as country],
aggr=[LAST_VALUE(sales_global.amount)]
SortExec: expr=[ts@1 DESC]
MemoryExec: partitions=1, partition_sizes=[1], output_ordering=[ts ASC]
```
However, if we were to treat above query in its equivalent for like below
```sql
SELECT country, FIRST_VALUE(amount ORDER BY ts ASC) AS lv1
FROM sales_global
GROUP BY country
```
we can produce following plan
```sql
ProjectionExec: expr=[country@0 as country, FIRST_VALUE(sales_global.amount)
ORDER BY [sales_global.ts ASC NULLS LAST]@1 as lv1]
AggregateExec: mode=Single, gby=[country@0 as country],
aggr=[LAST_VALUE(sales_global.amount)]
MemoryExec: partitions=1, partition_sizes=[1], output_ordering=[ts ASC]
```
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# What changes are included in this PR?
This PR analyzes reverse ordering requirements, both to resolve conflicting
ordering requirements and also remove away `SortExec`s from the physical plan,
if it is possible.
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# Are these changes tested?
Yes new tests are added to `groupby.slt` file.
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# Are there any user-facing changes?
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