danny0405 commented on a change in pull request #1121: [CALCITE-2936] Simplify
EXISTS or NOT EXISTS sub-query that has "GROUP BY ()"
URL: https://github.com/apache/calcite/pull/1121#discussion_r267804795
##########
File path: core/src/main/java/org/apache/calcite/sql2rel/SqlToRelConverter.java
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@@ -1165,8 +1165,22 @@ private void substituteSubQuery(Blackboard bb, SubQuery
subQuery) {
if (!config.isExpand()) {
return;
}
- converted = convertExists(query, RelOptUtil.SubQueryType.EXISTS,
- subQuery.logic, true, null);
+ final SqlValidatorScope seekScope =
+ (query instanceof SqlSelect)
+ ? validator.getSelectScope((SqlSelect) query)
+ : null;
+ final Blackboard seekBb = createBlackboard(seekScope, null, false);
+ final RelNode seekRel = convertQueryOrInList(seekBb, query, null);
+ // An existential sub-query whose inner child has at least 1 tuple
+ // (e.g. an Aggregate with no grouping columns or non-empty Values node)
+ // should be simplified to a Boolean constant expression.
+ final RelMetadataQuery mq = seekRel.getCluster().getMetadataQuery();
+ if (mq.getMinRowCount(seekRel) > 0.0) {
+ subQuery.expr = rexBuilder.makeLiteral(true);
Review comment:
Should we introduce statistics directly during sqlNode to RelNode converting
? Some how we can not make sure the statistics is definitely right, this may
causes wrong results. I think it's a little radical promotion.
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