... However, both Item_direct_view_ref and Item_singlerow_subselect have result_field=NULL.

result_field is set in create_tmp_table.
Looking at that function.
Note that EXPLAIN shows that table album has type= const.

create_tmp_table has this code:

  while ((item=li++))

  {

    Item::Type type=item->type();

    if (not_all_columns)

    {

       ...

      if (item->const_item() && (int) hidden_field_count <= 0)

        continue; // We don't have to store this

    }

We arrive to "We don't have to store this" for all items in albumview.*, including the iTimesPlayed subquery.

Items in the other table are also Item_direct_view objects, and create_tmp_table will call set_result_field for them:

(gdb) wher 4

  #0  Item_ref::set_result_field (this=0x7fff9c0400b0, field=0x7fff9c06c028) at /home/psergey/dev-git/10.0/sql/item.h:3439

  #1  0x00000000006cb079 in create_tmp_field (thd=0x2ed0960, table=0x7fff9c073bd8, item=0x7fff9c014740, type=Item::FIELD_ITEM, copy_func=0x7ffff7f80d80, from_field=0x7fff9c074d40, default_field=0x7fff9c074c18, group=false, modify_item=false, table_cant_handle_bit_fields=false, make_copy_field=false, convert_blob_length=0) at /home/psergey/dev-git/10.0/sql/sql_select.cc:15656

  #2  0x00000000006cc67d in create_tmp_table (thd=0x2ed0960, param=0x7fff9c03b9b0, fields=..., group=0x0, distinct=false, save_sum_fields=false, select_options=2147748608, rows_limit=18446744073709551615

.. however, change_refs_to_tmp_fields() seems to ignore the above difference. It has a loop that just goes through all items.

Need to discuss this with sanja.

revision-id: ad9ed479ab2cb711ce2b0de01f91eb03dfd0c4d6 (mariadb-10.0.21-59-gad9ed47)
parent(s): a9b5a8d5056af6c8f9b98a231ffa2de9ea20f215
committer: Oleksandr Byelkin
timestamp: 2015-10-28 08:34:08 +0100
message:

MDEV-8525 mariadb 10.0.20 crashing when data is read by Kodi media center (http://kodi.tv).

Item_direct_view_ref maintains its own item_const() method so should use it when asked of temporary table field to be in sync with it.

—

Ok to push.

I think we should ask elenst to make a test pass with RQG and relevant test load: queries with ORDER BY/GROUP BY/DISTINCT .