[GitHub] [calcite] dssysolyatin commented on a diff in pull request #2977: [CALCITE-5388] No result when using ROW_NUMBER in two common table expressions

[GitBox <gi...@apache.org>]

dssysolyatin commented on code in PR #2977:
URL: https://github.com/apache/calcite/pull/2977#discussion_r1033016387


##########
core/src/main/java/org/apache/calcite/adapter/enumerable/EnumerableWindow.java:
##########
@@ -693,7 +696,7 @@ private static Pair<Expression, Expression> getPartitionIterator(
     }
     Expression multiMap_ =
         builder.append(
-            "multiMap", Expressions.new_(SortedMultiMap.class));
+            "multiMap", Expressions.new_(SortedMultiMap.class), false);

Review Comment:
   multiMap works OK at the moment even with optimize = true. But it is very unsafe. I will try to explain why. The different between multiMap and tempList cases are following.
   
   Code for tempList case looks like:
   ```
   final java.util.List tempList = (java.util.List) org.apache.calcite.linq4j.Linq4j.asEnumerable(new Integer[] {1,2})
                                                                .into(new java.util.ArrayList()); <-- this expression will be reused.
   tempList.clear()
   <----> Second EnumerableWindow will use the same tempList and will not fill tempList again
   ```
   
   Code for multiMap looks like:
   ```
   final org.apache.calcite.runtime.SortedMultiMap multiMap = new org.apache.calcite.runtime.SortedMultiMap(); <--this expression will be reused
   org.apache.calcite.linq4j.Linq4j.asEnumerable(new Integer[] {1,2}).foreach(<code for multiMap filling>)
   multiMap.clear()
   <----> Second EnumerableWindow will refill 
   ```
   Code works OK for multiMap only because the creation and filling of the multiMap are in different expressions. But it is very unsafe. If for some reason creating and filling multiMap are in the same expression code will also stop working.



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