ankitsultana opened a new pull request, #16551:
URL: https://github.com/apache/pinot/pull/16551
### Summary
Minor improvement to pushdown collation from the enclosing Exchange to the
Lite Mode generated Sort.
This is good for queries like the following. Without this patch the
generated Sort only has a fetch and no collation.
```
SET useMultistageEngine = true;
SET usePhysicalOptimizer = true;
SET useLiteMode = true;
EXPLAIN PLAN FOR WITH ordered_events AS (
SELECT
cityName,
tripAmount,
ROW_NUMBER() OVER (
ORDER BY ts DESC
) as row_num
FROM userFactEvents
),
filtered_events AS (
SELECT
*
FROM ordered_events
WHERE row_num < 1000
)
SELECT
cityName,
SUM(tripAmount) as cityTotal
FROM filtered_events
GROUP BY cityName
```
The plan now for this query is:
```
Execution Plan
PhysicalAggregate(group=[{0}], agg#0=[$SUM0($1)], aggType=[DIRECT])
PhysicalFilter(condition=[<($3, 1000)])
PhysicalWindow(window#0=[window(order by [2 DESC] rows between UNBOUNDED
PRECEDING and CURRENT ROW aggs [ROW_NUMBER()])])
PhysicalExchange(exchangeStrategy=[SINGLETON_EXCHANGE], collation=[[2
DESC]])
PhysicalSort(fetch=[100000])
PhysicalProject(cityName=[$3], tripAmount=[$7], ts=[$9])
PhysicalTableScan(table=[[default, userFactEvents]])
```
### Test Plan
Added a UT and also verified on Quickstart.
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