englefly commented on code in PR #18784:
URL: https://github.com/apache/doris/pull/18784#discussion_r1196233623
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fe/fe-core/src/main/java/org/apache/doris/nereids/stats/StatsCalculator.java:
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@@ -464,6 +478,32 @@ private Statistics computeTopN(TopN topN) {
return stats.withRowCount(Math.min(stats.getRowCount(),
topN.getLimit()));
}
+ private Statistics computePartitionTopN(PartitionTopN partitionTopN) {
+ Statistics stats = groupExpression.childStatistics(0);
+ double rowCount = stats.getRowCount();
+ List<Expression> partitionKeys = partitionTopN.getPartitionKeys();
+ if (!partitionTopN.hasGlobalLimit() && !partitionKeys.isEmpty()) {
+ // If there is no global limit. So result for the cardinality
estimation is:
+ // NDV(partition key) * partitionLimit
+ Map<Expression, ColumnStatistic> childSlotToColumnStats =
stats.columnStatistics();
+ List<ColumnStatistic> partitionByKeyStats = partitionKeys.stream()
+ .filter(childSlotToColumnStats::containsKey)
+ .map(childSlotToColumnStats::get)
+ .filter(s -> !s.isUnKnown)
+ .collect(Collectors.toList());
+ if (partitionByKeyStats.isEmpty()) {
+ // all column stats are unknown, use default ratio
+ rowCount = rowCount * DEFAULT_COLUMN_NDV_RATION;
+ } else {
+ rowCount = Math.min(rowCount,
partitionByKeyStats.stream().map(s -> s.ndv)
+ .max(Double::compare).get());
+ }
+ } else {
+ rowCount = Math.min(rowCount, partitionTopN.getPartitionLimit());
+ }
+ return stats.withRowCount(rowCount);
Review Comment:
yes, we need to update column stats. if we do not know how to update col
stats, just use Statisitcs.updateRowCountOnly()
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