[#MDEV-22415] Single table UPDATE/DELETE doesn't use non-semijoin Materialization

Single-table UPDATE/DELETEs do not support Materialization (I mean non-semi-join one, for the issue with semi-joins, see ~~MDEV-7487~~).

  #0  JOIN::choose_subquery_plan (this=0x7ffc40017368, join_tables=3) at /home/psergey/dev-git/10.4-rel/sql/opt_subselect.cc:6467

  #1  0x0000555555db8ad8 in make_join_statistics (join=0x7ffc40017368, tables_list=..., keyuse_array=0x7ffc40017658) at /home/psergey/dev-git/10.4-rel/sql/sql\_select.cc:5590

  #2  0x0000555555dac671 in JOIN::optimize_inner (this=0x7ffc40017368) at /home/psergey/dev-git/10.4-rel/sql/sql_select.cc:2254

  #3  0x0000555555da9fb6 in JOIN::optimize (this=0x7ffc40017368) at /home/psergey/dev-git/10.4-rel/sql/sql\_select.cc:1601

  #4  0x0000555555d301ab in st_select_lex::optimize_unflattened_subqueries (this=0x7ffc40005470, const_only=false) at /home/psergey/dev-git/10.4-rel/sql/sql_lex.cc:4188

  #5  0x0000555555e701d2 in mysql_update (thd=0x7ffc40000d50, table_list=0x7ffc40012450, fields=..., values=..., conds=0x7ffc40016e80, order_num=0, order=0x0, limit=18446744073709551615, ignore=false, found_return=0x7fffdcbb0e70, updated_return=0x7fffdcbb0f30) at /home/psergey/dev-git/10.4-rel/sql/sql_update.cc:516

/*

        TODO: outer_join can be NULL for DELETE statements.

        How to compute its cost?

*/

      outer_lookup_keys= 1;

Here, we don't know how many times the subquery will be evaluated (if we assume it's evaluated once, Materialization doesn't make sense).

Can we figure out how many rows single-table UPDATE/DELETE is going to examine?
Not yet: mysql_update() calls optimize_unflattened_subqueries:

[MDEV-22415] Single table UPDATE/DELETE doesn't use non-semijoin Materialization Created: 2020-04-29 Updated: 2024-01-30
Status:	Open
Project:	MariaDB Server
Component/s:	Optimizer
Fix Version/s:	11.6

[MDEV-22415] Single table UPDATE/DELETE doesn't use non-semijoin Materialization Created: 2020-04-29 Updated: 2024-01-30