ddl: fix a bug that dropping primary key lead to implicit invisible primary key success (#19281)

Signed-off-by: wjhuang2016 <huangwenjun1997@gmail.com>

ddl/index.go

@@ -687,6 +687,21 @@ func checkDropIndex(t *meta.Meta, job *model.Job) (*model.TableInfo, *model.Inde
 		return nil, nil, autoid.ErrWrongAutoKey
 	}
 
+	// Check that drop primary index will not cause invisible implicit primary index.
+	newIndices := make([]*model.IndexInfo, 0, len(tblInfo.Indices))
+	for _, idx := range tblInfo.Indices {
+		if idx.Name.L != indexInfo.Name.L {
+			newIndices = append(newIndices, idx)
+		}
+	}
+	newTbl := tblInfo.Clone()
+	newTbl.Indices = newIndices
+	err = checkInvisibleIndexOnPK(newTbl)
+	if err != nil {
+		job.State = model.JobStateCancelled
+		return nil, nil, errors.Trace(err)
+	}
+
 	return tblInfo, indexInfo, nil
 }
 

ddl/serial_test.go

@@ -1379,6 +1379,8 @@ func (s *testSerialSuite) TestInvisibleIndex(c *C) {
 	tk.MustExec("insert into t6 values (1, 2)")
 	tk.MustQuery("select * from t6").Check(testkit.Rows("1 2"))
 	tk.MustGetErrCode("alter table t6 drop primary key", errno.ErrPKIndexCantBeInvisible)
+	res := tk.MustQuery("show index from t6 where Key_name='PRIMARY';")
+	c.Check(len(res.Rows()), Equals, 1)
 }
 
 func (s *testSerialSuite) TestCreateClusteredIndex(c *C) {