Re: [PR] [CALCITE-6650] Optimize the IN sub-query and SOME sub-query by Metada… [calcite]

["NobiGo (via GitHub)" <gi...@apache.org>]

NobiGo commented on code in PR #4022:
URL: https://github.com/apache/calcite/pull/4022#discussion_r1825678979


##########
core/src/main/java/org/apache/calcite/rel/rules/SubQueryRemoveRule.java:
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@@ -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:
   > I have the same concern as @dssysolyatin. Could we instead check whether it is an instance of `Values` and then call `Values.isEmpty`? (Which is how `PruneEmptyRules` works.)
   
   I think we can't. Now we apply `SubQueryRemoveRule` before `PruneEmptyRules`. so the sub-query is not a VALUES.



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