[CALCITE-6087] EnumerableSortedAggregate returns incorrect result when input is empty

• Type: Bug
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Affects Version/s: 1.35.0
• Component/s: core
• Assignee: Unassigned
• Reporter: Ruben Q L
• Created: 02/Nov/23 16:44
• Updated: 28/Feb/24 06:03

Description

Performing a MAX on an empty table (or on a table where we apply a filter which does not return any value) shall return NULL, we can verify this with our "standard" EnumerableAggregate operator:

  @Test void enumerableAggregateOnEmptyInput() {
    tester(false, new HrSchema())
        .query("select max(deptno) as m from emps where deptno>100")
        .explainContains(
            "EnumerableAggregate(group=[{}], m=[MAX($1)])\n"
            + "  EnumerableCalc(expr#0..4=[{inputs}], expr#5=[100], expr#6=[>($t1, $t5)], proj#0..4=[{exprs}], $condition=[$t6])\n"
            + "    EnumerableTableScan(table=[[s, emps]])")
        .returnsOrdered("m=null");
  }

However, if we use Hook.PLANNER to force the aggregation to be implemented via EnumerableSortedAggregate on the same query:

  @Test void enumerableSortedAggregateOnEmptyInput() {
    tester(false, new HrSchema())
        .query("select max(deptno) as m from emps where deptno>100")
        .withHook(Hook.PLANNER, (Consumer<RelOptPlanner>) planner -> {
          planner.removeRule(EnumerableRules.ENUMERABLE_AGGREGATE_RULE);
          planner.addRule(EnumerableRules.ENUMERABLE_SORTED_AGGREGATE_RULE);
        })
        .explainContains(
            "EnumerableSortedAggregate(group=[{}], m=[MAX($1)])\n"
            + "  EnumerableCalc(expr#0..4=[{inputs}], expr#5=[100], expr#6=[>($t1, $t5)], proj#0..4=[{exprs}], $condition=[$t6])\n"
            + "    EnumerableTableScan(table=[[s, emps]])")
        .returnsOrdered("m=null");
  }

It fails, because the EnumerableSortedAggregate returns an empty result set rather than NULL:

java.lang.AssertionError: 
Expected: "m=null"
     but: was ""

Issue Links

• is related to: CALCITE-4008 Implement Code generation for EnumerableSortedAggregate
• relates to: CALCITE-6089 EnumerableSortedAggregate fails with ClassCastException: class X cannot be cast to class org.apache.calcite.runtime.FlatLists$ComparableList