planner: keep unfoldable exprs when pruning columns for ORDER BY items

executor/sort_test.go

@@ -0,0 +1,46 @@
+// Copyright 2019 PingCAP, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package executor_test
+
+import (
+ . "github.com/pingcap/check"
+ "github.com/pingcap/tidb/util/testkit"
+)
+
+func (s *testSuite2) TestSortRand(c *C) {
+ tk := testkit.NewTestKit(c, s.store)
+ tk.MustExec("use test")
+ tk.MustExec("drop table if exists t")
+ tk.MustExec("create table t(a int, b int);")
+
+ tk.MustQuery("explain select a from t order by rand()").Check(testkit.Rows(
+ "Projection_8 10000.00 root test.t.a",
+ "└─Sort_4 10000.00 root col_1:asc",
+ " └─Projection_9 10000.00 root test.t.a, rand()",
+ " └─TableReader_7 10000.00 root data:TableScan_6",
+ " └─TableScan_6 10000.00 cop table:t, range:[-inf,+inf], keep order:false, stats:pseudo",
+ ))
+
+ tk.MustQuery("explain select a, b from t order by abs(2)").Check(testkit.Rows(
+ "TableReader_8 10000.00 root data:TableScan_7",
+ "└─TableScan_7 10000.00 cop table:t, range:[-inf,+inf], keep order:false, stats:pseudo"))
+
+ tk.MustQuery("explain select a from t order by abs(rand())+1").Check(testkit.Rows(
+ "Projection_8 10000.00 root test.t.a",
+ "└─Sort_4 10000.00 root col_1:asc",
+ " └─Projection_9 10000.00 root test.t.a, plus(abs(rand()), 1)",
+ " └─TableReader_7 10000.00 root data:TableScan_6",
+ " └─TableScan_6 10000.00 cop table:t, range:[-inf,+inf], keep order:false, stats:pseudo",
+ ))
+}

expression/column.go

@@ -125,7 +125,7 @@ func (col *CorrelatedColumn) IsCorrelated() bool {
 
 // ConstItem implements Expression interface.
 func (col *CorrelatedColumn) ConstItem() bool {
- return false
+ return true
 }
 
 // Decorrelate implements Expression interface.

planner/core/rule_column_pruning.go

@@ -139,6 +139,9 @@ func (ls *LogicalSort) PruneColumns(parentUsedCols []*expression.Column) error {
  for i := len(ls.ByItems) - 1; i >= 0; i-- {
  cols := expression.ExtractColumns(ls.ByItems[i].Expr)
  if len(cols) == 0 {
+ if !ls.ByItems[i].Expr.ConstItem() {
+ continue
+ }
  ls.ByItems = append(ls.ByItems[:i], ls.ByItems[i+1:]...)
  } else {
  parentUsedCols = append(parentUsedCols, cols...)