From 81cf95f7b1a27714257f34eaa8de761473d7768f Mon Sep 17 00:00:00 2001
From: tianjiqx <tianjiqx@126.com>
Date: Tue, 16 Oct 2018 14:47:46 +0800
Subject: [PATCH] elegant fix drop view panic

---
 planner/core/logical_plan_test.go   | 7 +++++++
 planner/core/planbuilder.go         | 5 +++--
 planner/core/preprocess_test.go     | 3 ---
 planner/core/rule_column_pruning.go | 2 +-
 4 files changed, 11 insertions(+), 6 deletions(-)

diff --git a/planner/core/logical_plan_test.go b/planner/core/logical_plan_test.go
index 2b4a4c9687273..6e7d2acf7ca25 100644
--- a/planner/core/logical_plan_test.go
+++ b/planner/core/logical_plan_test.go
@@ -1224,6 +1224,13 @@ func (s *testPlanSuite) TestColumnPruning(c *C) {
 				3: {"a"},
 			},
 		},
+		//issue 78333
+		{
+			sql: "drop view if exists v",
+			ans: map[int][]string{
+				1: {},
+			},
+		},
 	}
 	for _, tt := range tests {
 		comment := Commentf("for %s", tt.sql)
diff --git a/planner/core/planbuilder.go b/planner/core/planbuilder.go
index 28f7b25dbf1fa..56dc38ef291a9 100644
--- a/planner/core/planbuilder.go
+++ b/planner/core/planbuilder.go
@@ -227,8 +227,9 @@ func (b *PlanBuilder) buildDo(v *ast.DoStmt) (Plan, error) {
 			RetType:  expr.GetType(),
 		})
 	}
-	//make dual schema if not
-	var _ = dual.Schema()
+	if dual.schema == nil {
+		dual.schema = expression.NewSchema()
+	}
 	p.SetChildren(dual)
 	p.self = p
 	p.SetSchema(schema)
diff --git a/planner/core/preprocess_test.go b/planner/core/preprocess_test.go
index 15b7bd0d8240e..17deb8a09d48b 100644
--- a/planner/core/preprocess_test.go
+++ b/planner/core/preprocess_test.go
@@ -194,9 +194,6 @@ func (s *testValidatorSuite) TestValidator(c *C) {
 		{"select * from ( select 1 ) a, (select 2) b;", true, nil},
 		{"select * from (select * from ( select 1 ) a join (select 2) b) b join (select 3) a;", false, nil},
 		{"select * from (select 1 ) a , (select 2) b, (select * from (select 3) a join (select 4) b) c;", false, nil},
-
-		//issue 7833
-		{"drop view if exists v;", true, nil},
 	}
 
 	store, dom, err := newStoreWithBootstrap()
diff --git a/planner/core/rule_column_pruning.go b/planner/core/rule_column_pruning.go
index 933c93b206900..1bb66185a0973 100644
--- a/planner/core/rule_column_pruning.go
+++ b/planner/core/rule_column_pruning.go
@@ -167,7 +167,7 @@ func (ds *DataSource) PruneColumns(parentUsedCols []*expression.Column) {
 
 // PruneColumns implements LogicalPlan interface.
 func (p *LogicalTableDual) PruneColumns(parentUsedCols []*expression.Column) {
-	used := getUsedList(parentUsedCols, p.schema)
+	used := getUsedList(parentUsedCols, p.Schema())
 	for i := len(used) - 1; i >= 0; i-- {
 		if !used[i] {
 			p.schema.Columns = append(p.schema.Columns[:i], p.schema.Columns[i+1:]...)