planner: DELETE cannot delete data in some cases when the database name is capitalized (#21202)

executor/delete_test.go

@@ -0,0 +1,39 @@
+// Copyright 2020 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 *testSuite4) TestIssue21200(c *C) {
+	tk := testkit.NewTestKit(c, s.store)
+	tk.MustExec("drop database if exists TEST1")
+	tk.MustExec("create database TEST1")
+	tk.MustExec("use TEST1")
+	tk.MustExec("create table t(a int)")
+	tk.MustExec("create table t1(a int)")
+	tk.MustExec("insert into t values(1)")
+	tk.MustExec("insert into t1 values(1)")
+	tk.MustExec("delete a from t a where exists (select 1 from t1 where t1.a=a.a)")
+	tk.MustQuery("select * from t").Check(testkit.Rows())
+
+	tk.MustExec("insert into t values(1), (2)")
+	tk.MustExec("insert into t1 values(2)")
+	tk.MustExec("prepare stmt from 'delete a from t a where exists (select 1 from t1 where a.a=t1.a and t1.a=?)'")
+	tk.MustExec("set @a=1")
+	tk.MustExec("execute stmt using @a")
+	tk.MustQuery("select * from t").Check(testkit.Rows("2"))
+}

planner/core/logical_plan_builder.go

@@ -3005,12 +3005,12 @@ func (b *PlanBuilder) buildDelete(ctx context.Context, delete *ast.DeleteStmt) (
 		for _, tn := range delete.Tables.Tables {
 			foundMatch := false
 			for _, v := range tableList {
-				dbName := v.Schema.L
-				if dbName == "" {
-					dbName = b.ctx.GetSessionVars().CurrentDB
+				dbName := v.Schema
+				if dbName.L == "" {
+					dbName = model.NewCIStr(b.ctx.GetSessionVars().CurrentDB)
 				}
-				if (tn.Schema.L == "" || tn.Schema.L == dbName) && tn.Name.L == v.Name.L {
-					tn.Schema.L = dbName
+				if (tn.Schema.L == "" || tn.Schema.L == dbName.L) && tn.Name.L == v.Name.L {
+					tn.Schema = dbName
 					tn.DBInfo = v.DBInfo
 					tn.TableInfo = v.TableInfo
 					foundMatch = true