xzj7019 commented on code in PR #21428:
URL: https://github.com/apache/doris/pull/21428#discussion_r1255196550
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fe/fe-core/src/main/java/org/apache/doris/nereids/stats/StatsCalculator.java:
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@@ -680,11 +680,13 @@ private double estimateGroupByRowCount(List<Expression>
groupByExpressions, Stat
}
int groupByCount = groupByExpressions.size();
if
(groupByColStats.values().stream().anyMatch(ColumnStatistic::isUnKnown)) {
+ // if there is group-bys, output row count is
childStats.getRowCount() * DEFAULT_AGGREGATE_RATIO,
+ // o.w. output row count is 1
+ // example: select sum(A) from T;
if (groupByCount > 0) {
- rowCount *= DEFAULT_AGGREGATE_RATIO *
Math.pow(DEFAULT_AGGREGATE_EXPAND_RATIO, groupByCount - 1);
- }
- if (rowCount > childStats.getRowCount()) {
- rowCount = childStats.getRowCount();
+ rowCount = childStats.getRowCount() * DEFAULT_AGGREGATE_RATIO;
Review Comment:
after using childStats.getRowCount(), why discard original reasonable
radio Math.pow(DEFAULT_AGGREGATE_EXPAND_RATIO, groupByCount - 1)?
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