feat: support SELECT DISTINCT id FROM t ORDER BY id LIMIT n query use GroupedTopKAggregateStream
#19653
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… GroupedTopKAggregateStream
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logical-expr
haohuaijin
commented
Jan 10, 2026
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| let mut cols = self.priority_map.emit()?; | ||
| // For DISTINCT case (no aggregate expressions), only use the group key column | ||
| // since the schema only has one field and key/value are the same | ||
| if self.aggregate_arguments.is_empty() { | ||
| cols.truncate(1); | ||
| } |
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we can further improve this part, because for the query
select distinct id from t order by id limit 10it do not have any aggregate, so we only need mantain the topk heap, and skip the group keys
kosiew
approved these changes
Jan 14, 2026
| let batches = collect(plan, ctx.task_ctx()).await?; | ||
| assert_eq!(batches.len(), 1); | ||
| let batch = batches.first().unwrap(); | ||
| assert_eq!(batch.num_rows(), 10); |
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|
Thanks for your reviews @kosiew, already apply suggestion |
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Which issue does this PR close?
close #19638
Rationale for this change
see issue #19638
What changes are included in this PR?
LimitOptionsstruct limit field with bothlimitand optionaldescendingordering directionTopKAggregationoptimizer rule to DISTINCT queries by recognizingGROUP BYqueries without aggregates and setting thedescendingflag based on ordering directionGroupedTopKAggregateStreamto handle DISTINCT by using group key as both priority queue key and value for DISTINCT operationsdescendingfield toAggLimitmessage for serialization/deserializationbenchmark result
Are these changes tested?
yes, add test case in aggregates_topk.slt
Are there any user-facing changes?
no