From 0972a6f0129c21462eecd756b411c44e54d2ad17 Mon Sep 17 00:00:00 2001
From: lysu <sulifx@gmail.com>
Date: Mon, 15 Apr 2019 16:02:27 +0800
Subject: [PATCH] planner: keep unfoldable exprs when pruning columns for ORDER
 BY items (#10064)

---
 executor/sort_test.go               | 46 +++++++++++++++++++++++++++++
 expression/column.go                |  2 +-
 expression/column_test.go           |  2 +-
 planner/core/rule_column_pruning.go |  3 ++
 4 files changed, 51 insertions(+), 2 deletions(-)
 create mode 100644 executor/sort_test.go

diff --git a/executor/sort_test.go b/executor/sort_test.go
new file mode 100644
index 0000000000000..83da697db84ff
--- /dev/null
+++ b/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",
+	))
+}
diff --git a/expression/column.go b/expression/column.go
index 1c4ec9ab49bda..99b94e0ea4414 100644
--- a/expression/column.go
+++ b/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.
diff --git a/expression/column_test.go b/expression/column_test.go
index 5f0ffdb2c9b46..6d8e04e754227 100644
--- a/expression/column_test.go
+++ b/expression/column_test.go
@@ -43,7 +43,7 @@ func (s *testEvaluatorSuite) TestColumn(c *C) {
 	c.Assert(corCol.Equal(nil, corCol), IsTrue)
 	c.Assert(corCol.Equal(nil, invalidCorCol), IsFalse)
 	c.Assert(corCol.IsCorrelated(), IsTrue)
-	c.Assert(corCol.ConstItem(), IsFalse)
+	c.Assert(corCol.ConstItem(), IsTrue)
 	c.Assert(corCol.Decorrelate(schema).Equal(nil, col), IsTrue)
 	c.Assert(invalidCorCol.Decorrelate(schema).Equal(nil, invalidCorCol), IsTrue)
 
diff --git a/planner/core/rule_column_pruning.go b/planner/core/rule_column_pruning.go
index 34f74d1eca006..77651fffef1f8 100644
--- a/planner/core/rule_column_pruning.go
+++ b/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...)