LogicalPlans that contain Window Function are ambiguous

[An-DJ]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

1. add test case in planner/cascades/transformation_rules_test.go. The number of iterations can be greater than 100 :

   func (s *testTransformationRuleSuite) TestWindowLogicalPlan(c *C) {
   s.optimizer.ResetTransformationRules(map[memo.Operand][]Transformation{
       memo.OperandProjection: {
           NewRuleMergeAdjacentProjection(),
           NewRuleEliminateProjection(),
       },
   })
   defer func() {
       s.optimizer.ResetTransformationRules(DefaultRuleBatches...)
   }()
   input := "select a, max(a) over(), sum(a) over() from t"
   output1 := "DataScan(t)->Projection->Projection->Window(max(test.t.a)->Column#15)->Projection->Window(sum(cast(test.t.a, decimal(65,0) BINARY))->Column#16)->Projection"
   output2 := "DataScan(t)->Projection->Projection->Window(sum(cast(test.t.a, decimal(65,0) BINARY))->Column#15)->Projection->Window(max(test.t.a)->Column#16)->Projection"
   hasOut1 := false
   hasOut2 := false
   for i := 0; i < 100; i++ {
       stmt, err := s.ParseOneStmt(input, "", "")
       c.Assert(err, IsNil)
       p, _, err := plannercore.BuildLogicalPlan(context.Background(), s.sctx, stmt, s.is)
       str := plannercore.ToString(p)
       if str == output1{
           hasOut1 = true
       }
       if str == output2{
           hasOut2 = true
       }
   }
   fmt.Println(hasOut1, hasOut2)
   }

2. execute go test -check.f "testTransformationRuleSuite.TestWindowLogicalPlan" in path planner/cascades

2. What did you expect to see? (Required)

sql select a, max(a) over(), sum(a) over() from t should be built into only one LogicalPlan.

go test -check.f "testTransformationRuleSuite.TestWindowLogicalPlan" false true PASS: transformation_rules_test.go:528: testTransformationRuleSuite.TestWindowLogicalPlan 0.011s OK: 1 passed PASS ok github.com/pingcap/tidb/planner/cascades 0.132s

3. What did you see instead (Required)

sql select a, max(a) over(), sum(a) over() from t is built into two different LogicalPlans. go test -check.f "testTransformationRuleSuite.TestWindowLogicalPlan" true true PASS: transformation_rules_test.go:528: testTransformationRuleSuite.TestWindowLogicalPlan 0.011s OK: 1 passed PASS ok github.com/pingcap/tidb/planner/cascades 0.132s

4. What is your TiDB version? (Required)

code in branch master.

[ti-srebot]

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