Cannot DROP VERSIONING without dropping all visible AS ROW fields

mysql-test/suite/versioning/r/alter.result

@@ -64,6 +64,8 @@ t	CREATE TABLE `t` (
   `trx_end` timestamp(6) GENERATED ALWAYS AS ROW END INVISIBLE,
   PERIOD FOR SYSTEM_TIME (`trx_start`, `trx_end`)
 ) ENGINE=MyISAM DEFAULT CHARSET=latin1 WITH SYSTEM VERSIONING
+alter table t drop system versioning;
+ERROR HY000: System versioning field `trx_start` exists
 alter table t drop column trx_start, drop column trx_end;
 alter table t drop system versioning;
 show create table t;

mysql-test/suite/versioning/t/alter.test

@@ -53,6 +53,9 @@ alter table t
   add system versioning;
 show create table t;
 
+--error ER_VERS_SYS_FIELD_EXISTS
+alter table t drop system versioning;
+
 alter table t drop column trx_start, drop column trx_end;
 alter table t drop system versioning;
 show create table t;

sql/sql_table.cc

@@ -8009,6 +8009,13 @@ mysql_prepare_alter_table(THD *thd, TABLE *table,
 	def_it.remove();
       }
     }
+    else if (alter_info->flags & Alter_info::ALTER_DROP_SYSTEM_VERSIONING &&
+             field->flags & VERS_SYSTEM_FIELD &&
+             field->invisible < INVISIBLE_SYSTEM)
+    {
+      my_error(ER_VERS_SYS_FIELD_EXISTS, MYF(0), field->field_name.str);
+      goto err;
+    }
     else
     {
       /*