MDEV-27452 TIMESTAMP(0) system field is allowed for certain creation of system-versioned table

First, we do not add VERS_UPDATE_UNVERSIONED_FLAG for system field and
that fixes SHOW CREATE result.

Second, we have to call check_sys_fields() for any CREATE TABLE and
there correct type is checked for system fields.

Third, we update system_time like as_row structures for ALTER TABLE
and that makes check_sys_fields() happy for ALTER TABLE when we make
system fields hidden.

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

@@ -619,8 +619,32 @@ Table	Create Table
 t1	CREATE TABLE `t1` (
   `x` int(11) DEFAULT NULL WITHOUT SYSTEM VERSIONING,
   `y` int(11) DEFAULT NULL,
-  `row_start` timestamp(6) GENERATED ALWAYS AS ROW START WITHOUT SYSTEM VERSIONING,
-  `row_end` timestamp(6) GENERATED ALWAYS AS ROW END WITHOUT SYSTEM VERSIONING,
+  `row_start` timestamp(6) GENERATED ALWAYS AS ROW START,
+  `row_end` timestamp(6) GENERATED ALWAYS AS ROW END,
   PERIOD FOR SYSTEM_TIME (`row_start`, `row_end`)
 ) ENGINE=DEFAULT_ENGINE DEFAULT CHARSET=latin1 WITH SYSTEM VERSIONING
 drop table t1;
+#
+# MDEV-27452 TIMESTAMP(0) system field is allowed for certain creation of system-versioned table
+#
+create or replace table t (
+a int,
+s timestamp as row start,
+e timestamp as row end,
+period for system_time (s, e))
+with system versioning;
+ERROR HY000: `s` must be of type TIMESTAMP(6) for system-versioned table `t`
+create or replace table t (
+a int with system versioning,
+s timestamp as row start,
+e timestamp as row end,
+period for system_time (s, e));
+ERROR HY000: `s` must be of type TIMESTAMP(6) for system-versioned table `t`
+create or replace table t (
+a int with system versioning,
+b int with system versioning,
+s timestamp(6) as row start,
+e timestamp(6) as row end,
+period for system_time (s, e));
+insert into t () values (),();
+drop table t;

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

@@ -468,3 +468,32 @@ create or replace table t1 (
 show create table t1;
 
 drop table t1;
+
+--echo #
+--echo # MDEV-27452 TIMESTAMP(0) system field is allowed for certain creation of system-versioned table
+--echo #
+--error ER_VERS_FIELD_WRONG_TYPE
+create or replace table t (
+  a int,
+  s timestamp as row start,
+  e timestamp as row end,
+  period for system_time (s, e))
+with system versioning;
+
+--error ER_VERS_FIELD_WRONG_TYPE
+create or replace table t (
+  a int with system versioning,
+  s timestamp as row start,
+  e timestamp as row end,
+  period for system_time (s, e));
+
+create or replace table t (
+  a int with system versioning,
+  b int with system versioning,
+  s timestamp(6) as row start,
+  e timestamp(6) as row end,
+  period for system_time (s, e));
+insert into t () values (),();
+ 
+# cleanup
+drop table t;

sql/handler.cc

@@ -7226,6 +7226,8 @@ bool Table_scope_and_contents_source_st::vers_fix_system_fields(
   List_iterator<Create_field> it(alter_info->create_list);
   while (Create_field *f= it++)
   {
+    if (f->vers_sys_field())
+      continue;
     if ((f->versioning == Column_definition::VERSIONING_NOT_SET && !add_versioning) ||
         f->versioning == Column_definition::WITHOUT_VERSIONING)
     {
@@ -7247,9 +7249,10 @@ bool Table_scope_and_contents_source_st::vers_check_system_fields(
   if (!(options & HA_VERSIONED_TABLE))
     return false;
 
+  uint versioned_fields= 0;
+
   if (!(alter_info->flags & ALTER_DROP_SYSTEM_VERSIONING))
   {
-    uint versioned_fields= 0;
     uint fieldnr= 0;
     List_iterator<Create_field> field_it(alter_info->create_list);
     while (Create_field *f= field_it++)
@@ -7280,7 +7283,7 @@ bool Table_scope_and_contents_source_st::vers_check_system_fields(
     }
   }
 
-  if (!(alter_info->flags & ALTER_ADD_SYSTEM_VERSIONING))
+  if (!(alter_info->flags & ALTER_ADD_SYSTEM_VERSIONING) && !versioned_fields)
     return false;
 
   bool can_native= ha_check_storage_engine_flag(db_type,

sql/sql_table.cc

@@ -8230,9 +8230,14 @@ mysql_prepare_alter_table(THD *thd, TABLE *table,
       def->invisible= INVISIBLE_SYSTEM;
       alter_info->flags|= ALTER_CHANGE_COLUMN;
       if (field->flags & VERS_ROW_START)
-        create_info->vers_info.as_row.start= def->field_name= Vers_parse_info::default_start;
+        create_info->vers_info.system_time.start=
+          create_info->vers_info.as_row.start=
+          def->field_name= Vers_parse_info::default_start;
+
       else
-        create_info->vers_info.as_row.end= def->field_name= Vers_parse_info::default_end;
+        create_info->vers_info.system_time.end=
+          create_info->vers_info.as_row.end=
+          def->field_name= Vers_parse_info::default_end;
       new_create_list.push_back(def, thd->mem_root);
       dropped_sys_vers_fields|= field->flags;
       drop_it.remove();