let the ORDER BY case be decorrelated

expression/util.go

@@ -190,7 +190,7 @@ func ExtractColumnsAndCorColumnsFromExpressions(result []*Column, list []Express
 }
 
 // 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

@@ -154,7 +154,14 @@ func (s *decorrelateSolver) optimize(ctx context.Context, p LogicalPlan, opt *lo
 				return s.optimize(ctx, p, opt)
 			}
 		} else if proj, ok := innerPlan.(*LogicalProjection); ok {
-			if colSet := expression.ExtractColumnSet(proj.Exprs); colSet.IsEmpty() && apply.JoinType == LeftOuterJoin {
+			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.

planner/core/rule_partition_processor.go

@@ -930,7 +930,7 @@ 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_out.json

@@ -176,7 +176,7 @@
         "Err": false
       },
       {
-        "Best": "Apply{UnionAll{UnionAll{Dual->Projection->Dual->Projection}->Aggr(firstrow(Column#4))->Projection->Dual->Projection}->Dual->Projection}->Sort->Projection",
+        "Best": "Join{UnionAll{UnionAll{Dual->Projection->Dual->Projection}->Aggr(firstrow(Column#4))->Projection->Dual->Projection}->Dual}->Sort->Projection",
         "Err": false
       }
     ]

util/ranger/detacher.go

@@ -197,7 +197,7 @@ 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
 		}