github-actions[bot] commented on code in PR #68861:
URL: https://github.com/apache/doris/pull/68861#discussion_r4255946767
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fe/fe-core/src/main/java/org/apache/doris/nereids/rules/exploration/mv/AbstractMaterializedViewAggregateRule.java:
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@@ -588,6 +610,16 @@ private boolean isGroupByEquals(Pair<Plan,
LogicalAggregate<Plan>> queryTopPlanA
LogicalAggregate<Plan> queryAggregate = queryTopPlanAndAggPair.value();
LogicalAggregate<Plan> viewAggregate = viewTopPlanAndAggPair.value();
+ // If the query is a scalar aggregate but the view groups by extra
dimensions, the dimensions
+ // removed by the uniform function dependency below only guarantee at
most one group, not that a
+ // group exists. Eliminating the aggregate into a bare project would
lose the single row a scalar
+ // aggregate must always emit when the filter matches zero rows. Keep
the aggregate by rejecting
+ // this fast path and falling back to the roll up rewrite.
+ if (queryAggregate.getGroupByExpressions().isEmpty()
+ && !viewAggregate.getGroupByExpressions().isEmpty()) {
Review Comment:
[P1] Restore HAVING above the retained scalar aggregate
For an MV `select k, count(*) cnt from t group by k having count(*) > 0`,
consider `select count(*) from t where k = 9999 having count(*) > 0` when
k=9999 is absent. The reduced query is `Filter(c > 0) -> Aggregate([], COUNT(*)
AS c) -> Filter(k=9999) -> Scan(t)` and must return zero rows.
`Predicates.compensatePredicates` removes the identical aggregate HAVING as an
exact-covered residual before its unsafe-aggregate check. This new guard then
forces the rollup, but `aggregateRewriteByView` restores only outputs,
producing `Project(ifnull(s,0)) -> Aggregate([], SUM(mv.cnt) AS s) ->
Filter(mv.k=9999) -> MVScan` with no upper HAVING. That plan returns a row
containing 0; the previous aggregate-eliminating path returned zero rows.
Rebuild the query HAVING above the compensated scalar result, and cover this
case in the regression.
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