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MDEV-7487 Semi-join optimization for single-table update/delete statements

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This patch allows to use semi-join optimization at the top level of
single-table update and delete statements.
The problem of supporting such optimization became easy to resolve after
processing a single-table update/delete statement started using JOIN
structure. This allowed to use JOIN::prepare() not only for multi-table
updates/deletes but for single-table ones as well. This was done in the
patch for mdev-28883:
Re-design the upper level of handling UPDATE and DELETE statements.

Note that JOIN::prepare() detects all subqueries that can be considered
as candidates for semi-join optimization. The code added by this patch
looks for such candidates at the top level and if such candidates are found
in the processed single-table update/delete the statement is handled in
the same way as a multi-table update/delete.

    Approved by Oleksandr Byelkin <sanja@mariadb.com>
This commit is contained in:
Igor Babaev
2023-01-09 22:39:39 -08:00
parent e2e3524d72
commit 554278e24d
14 changed files with 6198 additions and 35 deletions
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5
sql/sql_delete.cc
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@ -348,7 +348,6 @@ bool Sql_cmd_delete::delete_from_single_table(THD *thd)
query_plan.using_filesort= FALSE;
THD_STAGE_INFO(thd, stage_init_update);
create_explain_query(thd->lex, thd->mem_root);
const bool delete_history= table_list->vers_conditions.delete_history;
DBUG_ASSERT(!(delete_history && table_list->period_conditions.is_set()));
@ -1668,6 +1667,10 @@ bool Sql_cmd_delete::prepare_inner(THD *thd)
{
goto err;
}
if (!multitable &&
select_lex->sj_subselects.elements)
multitable= true;
}
if (multitable)