cleanup: copy_data_between_tables()

don't read all columns from the source table, but only
those that the will be inserted into the target table
and cannot be generated by the target table.

test case is in the following commits

sql/sql_table.cc

@@ -10202,10 +10202,7 @@ copy_data_between_tables(THD *thd, TABLE *from, TABLE *to,
 
   alter_table_manage_keys(to, from->file->indexes_are_disabled(), keys_onoff);
 
-  /* Set read map for all fields in from table */
   from->default_column_bitmaps();
-  bitmap_set_all(from->read_set);
-  from->file->column_bitmaps_signal();
 
   /* We can abort alter table for any table type */
   thd->abort_on_warning= !ignore && thd->is_strict_mode();
@@ -10235,7 +10232,11 @@ copy_data_between_tables(THD *thd, TABLE *from, TABLE *to,
         if (def->field == from->found_next_number_field)
           thd->variables.sql_mode|= MODE_NO_AUTO_VALUE_ON_ZERO;
       }
-      (copy_end++)->set(*ptr,def->field,0);
+      if (!(*ptr)->vcol_info)
+      {
+        bitmap_set_bit(from->read_set, def->field->field_index);
+        (copy_end++)->set(*ptr,def->field,0);
+      }
     }
     else
     {
@@ -10304,6 +10305,11 @@ copy_data_between_tables(THD *thd, TABLE *from, TABLE *to,
     from_row_end= from->vers_end_field();
   }
 
+  if (from_row_end)
+    bitmap_set_bit(from->read_set, from_row_end->field_index);
+
+  from->file->column_bitmaps_signal();
+
   THD_STAGE_INFO(thd, stage_copy_to_tmp_table);
   /* Tell handler that we have values for all columns in the to table */
   to->use_all_columns();