ALTER TABLE ... DROP COLUMN sys_start should rename a "dropped" column

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

@@ -67,6 +67,8 @@ t	CREATE TABLE `t` (
 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;
+select row_start from t;
+row_start
 alter table t drop system versioning;
 show create table t;
 Table	Create Table
@@ -133,12 +135,17 @@ with system versioning;
 select * from t for system_time all;
 a
 alter table t drop column row_start;
-ERROR HY000: Wrong parameters for `t`: missing 'DROP COLUMN row_end'
+ERROR HY000: Wrong parameters for `t`: missing 'DROP COLUMN `row_end`'
 alter table t drop column row_end;
-ERROR HY000: Wrong parameters for `t`: missing 'DROP COLUMN row_start'
+ERROR HY000: Wrong parameters for `t`: missing 'DROP COLUMN `row_start`'
 alter table t drop column row_start, drop column row_end;
 select * from t for system_time all;
 a
+show create table t;
+Table	Create Table
+t	CREATE TABLE `t` (
+  `a` int(11) DEFAULT NULL
+) ENGINE=MyISAM DEFAULT CHARSET=latin1 WITH SYSTEM VERSIONING
 alter table t drop column row_start;
 ERROR 42000: Can't DROP COLUMN `row_start`; check that it exists
 alter table t drop column row_end;

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

@@ -65,7 +65,7 @@ period for system_time (sys_start, sys_end)
 ) engine innodb with system versioning;
 insert into t1 values (1);
 alter table t1 drop column sys_start, drop column sys_end;
-select sys_end = 18446744073709551615 as transaction_based from t1 for system_time all;
+select row_end = 18446744073709551615 as transaction_based from t1 for system_time all;
 transaction_based
 1
 drop table t1;

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

@@ -57,6 +57,7 @@ show create table t;
 alter table t drop system versioning;
 
 alter table t drop column trx_start, drop column trx_end;
+select row_start from t;
 alter table t drop system versioning;
 show create table t;
 
@@ -95,6 +96,7 @@ alter table t drop column row_start;
 alter table t drop column row_end;
 alter table t drop column row_start, drop column row_end;
 select * from t for system_time all;
+show create table t;
 
 --error ER_CANT_DROP_FIELD_OR_KEY
 alter table t drop column row_start;

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

@@ -69,7 +69,7 @@ create or replace table t1 (
 ) engine innodb with system versioning;
 insert into t1 values (1);
 alter table t1 drop column sys_start, drop column sys_end;
-select sys_end = 18446744073709551615 as transaction_based from t1 for system_time all;
+select row_end = 18446744073709551615 as transaction_based from t1 for system_time all;
 
 drop table t1;
 drop function check_result;

sql/handler.cc

@@ -7283,60 +7283,6 @@ bool Vers_parse_info::fix_alter_info(THD *thd, Alter_info *alter_info,
       }
     }
 
-    if (alter_info->drop_list.elements)
-    {
-      bool done_start= false;
-      bool done_end= false;
-      List_iterator<Alter_drop> it(alter_info->drop_list);
-      while (Alter_drop *d= it++)
-      {
-        const char *name= d->name;
-        Field *f= NULL;
-        if (!done_start && is_start(name))
-        {
-          f= share->vers_start_field();
-          done_start= true;
-        }
-        else if (!done_end && is_end(name))
-        {
-          f= share->vers_end_field();
-          done_end= true;
-        }
-        else
-          continue;
-        if (f->invisible > INVISIBLE_USER)
-        {
-          my_error(ER_CANT_DROP_FIELD_OR_KEY, MYF(0), d->type_name(), name);
-          return true;
-        }
-
-        bool integer= table->vers_start_field()->type() == MYSQL_TYPE_LONGLONG;
-        Create_field *field= vers_init_sys_field(thd, name, f->flags & VERS_SYSTEM_FIELD, integer);
-        if (!field)
-          return true;
-
-        field->change= f->field_name;
-
-        alter_info->flags|= Alter_info::ALTER_CHANGE_COLUMN;
-        alter_info->create_list.push_back(field);
-
-        it.remove();
-
-        if (done_start && done_end)
-          break;
-      }
-
-      if ((done_start || done_end) && done_start != done_end)
-      {
-        String tmp;
-        tmp.append("DROP COLUMN ");
-        tmp.append(done_start ? &table->vers_end_field()->field_name
-                              : &table->vers_start_field()->field_name);
-        my_error(ER_MISSING, MYF(0), table_name, tmp.c_ptr());
-        return true;
-      }
-    }
-
     return false;
   }
 
@@ -7369,7 +7315,7 @@ Vers_parse_info::fix_create_like(Alter_info &alter_info, HA_CREATE_INFO &create_
     int remove= 2;
     while (remove && (f= it++))
     {
-      if (f->flags & (VERS_SYS_START_FLAG|VERS_SYS_END_FLAG))
+      if (f->flags & VERS_SYSTEM_FIELD)
       {
         it.remove();
         remove--;

sql/sql_table.cc

@@ -7868,7 +7868,7 @@ mysql_prepare_alter_table(THD *thd, TABLE *table,
   List<Virtual_column_info> new_constraint_list;
   uint db_create_options= (table->s->db_create_options
                            & ~(HA_OPTION_PACK_RECORD));
-  uint used_fields;
+  uint used_fields, dropped_sys_vers_fields= 0;
   KEY *key_info=table->key_info;
   bool rc= TRUE;
   bool modified_primary_key= FALSE;
@@ -7950,7 +7950,15 @@ mysql_prepare_alter_table(THD *thd, TABLE *table,
           !my_strcasecmp(system_charset_info,field->field_name.str, drop->name))
         break;
     }
-    if (drop && field->invisible < INVISIBLE_SYSTEM)
+    /*
+      DROP COLULMN xxx
+      1. it does not see INVISIBLE_SYSTEM columns
+      2. otherwise, normally a column is dropped
+      3. unless it's a system versioning column (but see below).
+    */
+    if (drop && field->invisible < INVISIBLE_SYSTEM &&
+        !(field->flags & VERS_SYSTEM_FIELD &&
+          !(alter_info->flags & Alter_info::ALTER_DROP_SYSTEM_VERSIONING)))
     {
       /* Reset auto_increment value if it was dropped */
       if (MTYP_TYPENR(field->unireg_check) == Field::NEXT_NUMBER &&
@@ -7966,7 +7974,8 @@ mysql_prepare_alter_table(THD *thd, TABLE *table,
       bitmap_set_bit(dropped_fields, field->field_index);
       continue;
     }
-    if (!drop && field->invisible == INVISIBLE_SYSTEM &&
+    /* invisible versioning column is dropped automatically on DROP SYSTEM VERSIONING */
+    if (!drop && field->invisible >= INVISIBLE_SYSTEM &&
         field->flags & VERS_SYSTEM_FIELD &&
         alter_info->flags & Alter_info::ALTER_DROP_SYSTEM_VERSIONING)
     {
@@ -8016,6 +8025,22 @@ mysql_prepare_alter_table(THD *thd, TABLE *table,
       my_error(ER_VERS_SYS_FIELD_EXISTS, MYF(0), field->field_name.str);
       goto err;
     }
+    else if (drop && field->invisible < INVISIBLE_SYSTEM &&
+             field->flags & VERS_SYSTEM_FIELD &&
+             !(alter_info->flags & Alter_info::ALTER_DROP_SYSTEM_VERSIONING))
+    {
+      /* "dropping" a versioning field only hides it from the user */
+      def= new (thd->mem_root) Create_field(thd, field, field);
+      def->invisible= INVISIBLE_SYSTEM;
+      dropped_sys_vers_fields|= field->flags;
+      alter_info->flags|= Alter_info::ALTER_CHANGE_COLUMN;
+      if (field->flags & VERS_SYS_START_FLAG)
+        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;
+      new_create_list.push_back(def, thd->mem_root);
+      drop_it.remove();
+    }
     else
     {
       /*
@@ -8042,6 +8067,18 @@ mysql_prepare_alter_table(THD *thd, TABLE *table,
       }
     }
   }
+  if (dropped_sys_vers_fields &&
+      ((dropped_sys_vers_fields & VERS_SYSTEM_FIELD) != VERS_SYSTEM_FIELD))
+  {
+    StringBuffer<NAME_LEN*2> tmp;
+    tmp.append(STRING_WITH_LEN("DROP COLUMN "));
+    if (dropped_sys_vers_fields & VERS_SYS_START_FLAG)
+      append_identifier(thd, &tmp, &table->vers_end_field()->field_name);
+    else
+      append_identifier(thd, &tmp, &table->vers_start_field()->field_name);
+    my_error(ER_MISSING, MYF(0), table->s->table_name.str, tmp.c_ptr());
+    goto err;
+  }
   def_it.rewind();
   while ((def=def_it++))			// Add new columns
   {