[FLINK-22455] FlinkRelBuilder#windowAggregate will throw ClassCastException when function reuse

• Type: Bug
• Status: Open
• Priority: Not a Priority
• Resolution: Unresolved
• Component/s: Table SQL / Planner
• Labels: auto-deprioritized-major auto-deprioritized-minor
• Assignee: Unassigned
• Reporter: tartarus
• Created: 25/Apr/21 14:03
• Updated: 17/Mar/22 10:44

Description

If the input parameter aggCalls of FlinkRelBuilder#windowAggregate contains the same aggregate function. Then it will throw ClassCastException, because of the optimization of aggregate function reuse. We did not judge the return value type, but direct type conversion;

    val aggregate = super.transform(
      new UnaryOperator[RelBuilder.Config] {
        override def apply(t: RelBuilder.Config)
          : RelBuilder.Config = t.withPruneInputOfAggregate(false)
      })
      .push(build())
      .aggregate(groupKey, aggCalls)
      .build()
      .asInstanceOf[LogicalAggregate]

I wrote a test that triggered this problem.
You can use the attached code to reproduce this problem.