database/mariadb
1
0
Fork 0
mirror of https://github.com/MariaDB/server.git synced 2025-07-27 18:02:13 +03:00
Code Activity

MDEV-25128 Wrong result from join with materialized semi-join and

Browse Source 
splittable derived

If one of joined tables of the processed query is a materialized derived
table (or view or CTE) with GROUP BY clause then under some conditions it
can be subject to split optimization. With this optimization new equalities
are injected into the WHERE condition of the SELECT that specifies this
derived table. The injected equalities are generated for all join orders
with which the split optimization can employed. After the best join order
has been chosen only certain of this equalities are really needed. The
others can be safely removed. If it's not done and some of injected
equalities involve expressions over semi-joins with look-up access then
the query may return a wrong result set.
This patch effectively removes equalities injected for split optimization
that are needed only at the optimization stage and not needed for execution.

Approved by serg@mariadb.com
This commit is contained in:
Igor Babaev
2021-03-23 20:54:54 -07:00
parent 7d5ec9f1ae
commit 480a06718d
4 changed files with 307 additions and 6 deletions
Download Patch File Download Diff File Expand all files Collapse all files

17
sql/sql_select.cc
View File

@ -292,6 +292,8 @@ void set_postjoin_aggr_write_func(JOIN_TAB *tab);
static Item **get_sargable_cond(JOIN *join, TABLE *table);
bool is_eq_cond_injected_for_split_opt(Item_func_eq *eq_item);
#ifndef DBUG_OFF
/*
@ -21787,6 +21789,21 @@ make_cond_for_table_from_pred(THD *thd, Item *root_cond, Item *cond,
cond->marker=3; // Checked when read
return (COND*) 0;
}
/*
If cond is an equality injected for split optimization then
a. when retain_ref_cond == false : cond is removed unconditionally
(cond that supports ref access is removed by the preceding code)
b. when retain_ref_cond == true : cond is removed if it does not
support ref access
*/
if (left_item->type() == Item::FIELD_ITEM &&
is_eq_cond_injected_for_split_opt((Item_func_eq *) cond) &&
(!retain_ref_cond ||
!test_if_ref(root_cond, (Item_field*) left_item,right_item)))
{
cond->marker=3;
return (COND*) 0;
}
}
cond->marker=2;
cond->set_join_tab_idx(join_tab_idx_arg);