planner: don't decorrelate the APPLY when the inner's projection reference no column (#32370)

expression/util.go

@@ -165,7 +165,7 @@ func extractColumns(result []*Column, expr Expression, filter func(*Column) bool
 }
 
 // ExtractColumnSet extracts the different values of `UniqueId` for columns in expressions.
-func ExtractColumnSet(exprs []Expression) *intsets.Sparse {
+func ExtractColumnSet(exprs ...Expression) *intsets.Sparse {
  set := &intsets.Sparse{}
  for _, expr := range exprs {
  extractColumnSet(expr, set)

planner/core/rule_decorrelate.go

@@ -146,6 +146,21 @@ func (s *decorrelateSolver) optimize(ctx context.Context, p LogicalPlan) (Logica
  return s.optimize(ctx, p)
  }
  } else if proj, ok := innerPlan.(*LogicalProjection); ok {
+ allConst := true
+ for _, expr := range proj.Exprs {
+ if len(expression.ExtractCorColumns(expr)) > 0 || !expression.ExtractColumnSet(expr).IsEmpty() {
+ allConst = false
+ break
+ }
+ }
+ if allConst && apply.JoinType == LeftOuterJoin {
+ // If the projection just references some constant. We cannot directly pull it up when the APPLY is an outer join.
+ // e.g. select (select 1 from t1 where t1.a=t2.a) from t2; When the t1.a=t2.a is false the join's output is NULL.
+ // But if we pull the projection upon the APPLY. It will return 1 since the projection is evaluated after the join.
+ // We disable the decorrelation directly for now.
+ // TODO: Actually, it can be optimized. We need to first push the projection down to the selection. And then the APPLY can be decorrelated.
+ goto NoOptimize
+ }
  for i, expr := range proj.Exprs {
  proj.Exprs[i] = expr.Decorrelate(outerPlan.Schema())
  }
@@ -296,6 +311,7 @@ func (s *decorrelateSolver) optimize(ctx context.Context, p LogicalPlan) (Logica
  return s.optimize(ctx, p)
  }
  }
+NoOptimize:
  newChildren := make([]LogicalPlan, 0, len(p.Children()))
  for _, child := range p.Children() {
  np, err := s.optimize(ctx, child)

planner/core/rule_partition_processor.go

@@ -920,7 +920,7 @@ func makePartitionByFnCol(sctx sessionctx.Context, columns []*expression.Column,
  monotonous = getMonotoneMode(raw.FuncName.L)
  // Check the partitionExpr is in the form: fn(col, ...)
  // There should be only one column argument, and it should be the first parameter.
- if expression.ExtractColumnSet(args).Len() == 1 {
+ if expression.ExtractColumnSet(args...).Len() == 1 {
  if col1, ok := args[0].(*expression.Column); ok {
  col = col1
  }

planner/core/testdata/plan_suite_unexported_in.json

@@ -131,7 +131,8 @@
  "select t1.b from t t1 where t1.b in (select t2.b from t t2 where t2.a = t1.a order by t2.a)",
  "select t1.b from t t1 where exists(select t2.b from t t2 where t2.a = t1.a order by t2.a)",
  // `Sort` will not be eliminated, if it is not the top level operator.
- "select t1.b from t t1 where t1.b = (select t2.b from t t2 where t2.a = t1.a order by t2.a limit 1)"
+ "select t1.b from t t1 where t1.b = (select t2.b from t t2 where t2.a = t1.a order by t2.a limit 1)",
+ "select (select 1 from t t1 where t1.a = t2.a) from t t2"
  ]
  },
  {

planner/core/testdata/plan_suite_unexported_out.json

@@ -117,7 +117,8 @@
  "Join{DataScan(t1)->DataScan(t2)->Aggr(max(test.t.a),firstrow(test.t.b))}(test.t.b,test.t.b)->Projection->Sel([eq(test.t.b, Column#25)])->Projection",
  "Join{DataScan(t1)->DataScan(t2)}(test.t.a,test.t.a)(test.t.b,test.t.b)->Projection",
  "Join{DataScan(t1)->DataScan(t2)}(test.t.a,test.t.a)->Projection",
- "Apply{DataScan(t1)->DataScan(t2)->Sel([eq(test.t.a, test.t.a)])->Projection->Sort->Limit}->Projection->Sel([eq(test.t.b, test.t.b)])->Projection"
+ "Apply{DataScan(t1)->DataScan(t2)->Sel([eq(test.t.a, test.t.a)])->Projection->Sort->Limit}->Projection->Sel([eq(test.t.b, test.t.b)])->Projection",
+ "Apply{DataScan(t2)->DataScan(t1)->Sel([eq(test.t.a, test.t.a)])->Projection}->Projection"
  ]
  },
  {

util/ranger/detacher.go

@@ -196,7 +196,7 @@ func extractIndexPointRangesForCNF(sctx sessionctx.Context, conds []expression.E
  offset := int(-1)
  for i, cond := range conds {
  tmpConds := []expression.Expression{cond}
- colSets := expression.ExtractColumnSet(tmpConds)
+ colSets := expression.ExtractColumnSet(cond)
  if colSets.Len() == 0 {
  continue
  }