zabetak commented on code in PR #4022:
URL: https://github.com/apache/calcite/pull/4022#discussion_r1824963935
##########
core/src/main/java/org/apache/calcite/rel/rules/SubQueryRemoveRule.java:
##########
@@ -170,6 +170,13 @@ private static RexNode rewriteCollection(RexSubQuery e,
*/
private static RexNode rewriteSome(RexSubQuery e, Set<CorrelationId>
variablesSet,
RelBuilder builder, int subQueryIndex) {
+ // If the sub-query is guaranteed to return 0 row, just return
+ // FALSE.
+ final RelMetadataQuery mq = e.rel.getCluster().getMetadataQuery();
+ final Double maxRowCount = mq.getMaxRowCount(e.rel);
+ if (maxRowCount != null && maxRowCount < 1D) {
Review Comment:
```
/**
* Estimates the max number of rows which will be returned by a
relational
* expression.
*
* <p>The default implementation for this query returns
* {@link Double#POSITIVE_INFINITY},
* but metadata providers can override this with their own cost models.
*
* @return upper bound on the number of rows returned
*/
```
I would say that the Javadoc is already explicit.
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