SQL: prohibit column conversion to system fields for non-empty table [fixes #310]

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

@@ -593,6 +593,19 @@ alter table t add column b int;
 select * from t for system_time all;
 a	b
 2	NULL
+create or replace table non_empty (
+a int,
+sys_trx_start bigint(20) unsigned,
+sys_trx_end bigint(20) unsigned
+) engine innodb;
+insert into non_empty values (1, 100, 200);
+alter table non_empty
+change column sys_trx_start sys_trx_start bigint(20) unsigned generated always as row start;
+ERROR HY000: Can not modify column `sys_trx_start` to GENERATED ALWAYS AS ROW START/END for non-empty table
+alter table non_empty
+change column sys_trx_end sys_trx_end bigint(20) unsigned generated always as row end;
+ERROR HY000: Can not modify column `sys_trx_end` to GENERATED ALWAYS AS ROW START/END for non-empty table
+drop table non_empty;
 call verify_vtq;
 No	A	B	C	D
 1	1	1	1	1

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

@@ -282,6 +282,21 @@ select * from t for system_time all;
 alter table t add column b int;
 select * from t for system_time all;
 
+create or replace table non_empty (
+  a int,
+  sys_trx_start bigint(20) unsigned,
+  sys_trx_end bigint(20) unsigned
+) engine innodb;
+insert into non_empty values (1, 100, 200);
+
+--error ER_VERS_GENERATED_ALWAYS_NOT_EMPTY
+alter table non_empty
+  change column sys_trx_start sys_trx_start bigint(20) unsigned generated always as row start;
+--error ER_VERS_GENERATED_ALWAYS_NOT_EMPTY
+alter table non_empty
+  change column sys_trx_end sys_trx_end bigint(20) unsigned generated always as row end;
+drop table non_empty;
+
 call verify_vtq;
 drop table t;
 

sql/handler.cc

@@ -6913,8 +6913,9 @@ static bool add_field_to_drop_list(THD *thd, Alter_info *alter_info,
 
 bool Vers_parse_info::check_and_fix_alter(THD *thd, Alter_info *alter_info,
                                           HA_CREATE_INFO *create_info,
-                                          TABLE_SHARE *share)
+                                          TABLE *table)
 {
+  TABLE_SHARE *share= table->s;
   bool integer_fields=
       create_info->db_type->flags & HTON_NATIVE_SYS_VERSIONING;
   const char *table_name= share->table_name.str;
@@ -6950,6 +6951,29 @@ bool Vers_parse_info::check_and_fix_alter(THD *thd, Alter_info *alter_info,
     return false;
   }
 
+  {
+    List_iterator_fast<Create_field> it(alter_info->create_list);
+    while (Create_field *f= it++)
+    {
+      if (f->change.length &&
+          f->flags & (VERS_SYS_START_FLAG | VERS_SYS_END_FLAG))
+      {
+        if (thd->mdl_context.upgrade_shared_lock(
+                table->mdl_ticket, MDL_EXCLUSIVE,
+                thd->variables.lock_wait_timeout))
+          return true;
+        if (table->file->info(HA_STATUS_VARIABLE | HA_STATUS_TIME))
+          return true;
+        if (0 < table->file->records())
+        {
+          my_error(ER_VERS_GENERATED_ALWAYS_NOT_EMPTY, MYF(0), f->change.str);
+          return true;
+        }
+        break;
+      }
+    }
+  }
+
   if ((versioned_fields || unversioned_fields) && !share->versioned)
   {
     my_error_as(ER_VERS_WRONG_PARAMS, ER_VERS_NOT_VERSIONED, MYF(0), table_name);

sql/handler.h

@@ -1745,7 +1745,7 @@ struct Vers_parse_info
                               HA_CREATE_INFO *create_info,
                               const char *table_name);
   bool check_and_fix_alter(THD *thd, Alter_info *alter_info,
-                           HA_CREATE_INFO *create_info, TABLE_SHARE *share);
+                           HA_CREATE_INFO *create_info, TABLE *table);
   bool fix_create_like(THD *thd, Alter_info *alter_info,
                        HA_CREATE_INFO *create_info, TABLE_LIST *table);
 

sql/share/errmsg-utf8.txt

@@ -7907,3 +7907,6 @@ ER_VERS_SYS_FIELD_NOT_HIDDEN
 
 ER_NOT_LOG_TABLE
         eng "Table `%s.%s` is not a log table"
+
+ER_VERS_GENERATED_ALWAYS_NOT_EMPTY
+        eng "Can not modify column `%s` to GENERATED ALWAYS AS ROW START/END for non-empty table"

sql/sql_table.cc

@@ -8977,7 +8977,7 @@ bool mysql_alter_table(THD *thd, const char *new_db, const char *new_name,
     DBUG_RETURN(true);
 
   if (create_info->vers_info.check_and_fix_alter(thd, alter_info, create_info,
-                                                 table->s))
+                                                 table))
   {
     DBUG_RETURN(true);
   }