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Add description for MinMaxByToWindowFunction optimizer #25249

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Merged
feilong-liu merged 1 commit into from
Jun 5, 2025
Merged

Add description for MinMaxByToWindowFunction optimizer #25249

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28 changes: 28 additions & 0 deletions ...rc/main/java/com/facebook/presto/sql/planner/iterative/rule/MinMaxByToWindowFunction.java
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Original file line number Diff line number Diff line change
Expand Up @@ -47,6 +47,34 @@
import static com.facebook.presto.sql.relational.Expressions.comparisonExpression;
import static com.google.common.collect.ImmutableMap.toImmutableMap;

/**
* For queries with min_by/max_by functions on map, rewrite it with top n window functions.
* For example, for query `select id, max(ds), max_by(feature, ds) from t group by id`,
* it will be rewritten from:
* <pre>
* - Aggregation
* ds_0 := max(ds)
* feature_0 := max_by(feature, ds)
* group by id
* - scan t
* ds
* feature
* id
* </pre>
* into:
* <pre>
* - Filter
* row_num = 1
* - TopNRow
* partition by id
* order by ds desc
* maxRowCountPerPartition = 1
* - scan t
* ds
* feature
* id
* </pre>
*/
public class MinMaxByToWindowFunction
implements Rule<AggregationNode>
{
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