From ce87b6c6713d551b3700ea9732cd0955a3819952 Mon Sep 17 00:00:00 2001
From: Lynn <zimu_xia@126.com>
Date: Thu, 21 Nov 2019 17:24:10 +0800
Subject: [PATCH] ddl: fix the error message for dropping primary key (#13665)

---
 ddl/ddl_api.go     |  3 ++-
 ddl/serial_test.go | 20 ++++++++++++++++++++
 2 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/ddl/ddl_api.go b/ddl/ddl_api.go
index 764bcfc242..7d0c7e1dd6 100644
--- a/ddl/ddl_api.go
+++ b/ddl/ddl_api.go
@@ -3582,7 +3582,8 @@ func (d *ddl) dropIndex(ctx sessionctx.Context, ti ast.Ident, isPK bool, indexNa
 			return ErrUnsupportedModifyPrimaryKey.GenWithStack("Unsupported drop primary key when alter-primary-key is false")
 
 		}
-		if indexInfo == nil {
+		// If the table's PKIsHandle is true, we can't find the index from the table. So we check the value of PKIsHandle.
+		if indexInfo == nil && !t.Meta().PKIsHandle {
 			return ErrCantDropFieldOrKey.GenWithStack("Can't DROP 'PRIMARY'; check that column/key exists")
 		}
 		if t.Meta().PKIsHandle {
diff --git a/ddl/serial_test.go b/ddl/serial_test.go
index f1e2c0ce61..d12cd0e8a3 100644
--- a/ddl/serial_test.go
+++ b/ddl/serial_test.go
@@ -91,6 +91,26 @@ func (s *testSerialSuite) TestPrimaryKey(c *C) {
 	c.Assert(ddl.ErrUnsupportedModifyPrimaryKey.Equal(err), IsTrue)
 	_, err = tk.Exec("alter table primary_key_test drop primary key")
 	c.Assert(err.Error(), Equals, "[ddl:8200]Unsupported drop primary key when alter-primary-key is false")
+
+	// Change the value of AlterPrimaryKey.
+	tk.MustExec("create table primary_key_test1 (a int, b varchar(10), primary key(a))")
+	tk.MustExec("create table primary_key_test2 (a int, b varchar(10), primary key(b))")
+	tk.MustExec("create table primary_key_test3 (a int, b varchar(10))")
+	cfg := config.GetGlobalConfig()
+	newCfg := *cfg
+	orignalAlterPrimaryKey := newCfg.AlterPrimaryKey
+	newCfg.AlterPrimaryKey = true
+	config.StoreGlobalConfig(&newCfg)
+	defer func() {
+		newCfg.AlterPrimaryKey = orignalAlterPrimaryKey
+		config.StoreGlobalConfig(&newCfg)
+	}()
+
+	_, err = tk.Exec("alter table primary_key_test1 drop primary key")
+	c.Assert(err.Error(), Equals, "[ddl:8200]Unsupported drop primary key when the table's pkIsHandle is true")
+	tk.MustExec("alter table primary_key_test2 drop primary key")
+	_, err = tk.Exec("alter table primary_key_test3 drop primary key")
+	c.Assert(err.Error(), Equals, "[ddl:1091]Can't DROP 'PRIMARY'; check that column/key exists")
 }
 
 func (s *testSerialSuite) TestMultiRegionGetTableEndHandle(c *C) {