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MDEV-12387 Push conditions into materialized subqueries

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The logic and the implementation scheme are similar with the
MDEV-9197 Pushdown conditions into non-mergeable views/derived tables

How the push down is made on the example:

select * from t1
where a>3 and b>10 and
 (a,b) in (select x,max(y) from t2 group by x);

-->

select * from t1
where a>3 and b>10 and
  (a,b) in (select x,max(y)
            from t2
            where x>3
            group by x
            having max(y)>10);

The implementation scheme:

1. Search for the condition cond that depends only on the fields
   from the left part of the IN subquery (left_part)
2. Find fields F_group in the select of the right part of the
   IN subquery (right_part) that are used in the GROUP BY
3. Extract from the cond condition cond_where that depends only on the
   fields from the left_part that stay at the same places in the left_part
   (have the same indexes) as the F_group fields in the projection of the
   right_part
4. Transform cond_where so it can be pushed into the WHERE clause of the
   right_part and delete cond_where from the cond
5. Transform cond so it can be pushed into the HAVING clause of the right_part

The optimization is made in the
Item_in_subselect::pushdown_cond_for_in_subquery() and is controlled by the
variable condition_pushdown_for_subquery.

New test file in_subq_cond_pushdown.test is created.

There are also some changes made for setup_jtbm_semi_joins().
Now it is decomposed into the 2 procedures: setup_degenerate_jtbm_semi_joins()
that is called before optimize_cond() for cond and setup_jtbm_semi_joins()
that is called after optimize_cond().
New setup_jtbm_semi_joins() is made in the way so that the result of its work is
the same as if it was called before optimize_cond().

The code that is common for pushdown into materialized derived and into materialized
IN subqueries is factored out into pushdown_cond_for_derived(),
Item_in_subselect::pushdown_cond_for_in_subquery() and
st_select_lex::pushdown_cond_into_where_clause().
This commit is contained in:
Galina Shalygina
2018-05-15 23:45:59 +02:00
parent 569e3ad1ea
commit d3ff133390
30 changed files with 6115 additions and 504 deletions
Download Patch File Download Diff File Expand all files Collapse all files

56
sql/sql_select.cc
View File

@ -1616,10 +1616,29 @@ JOIN::optimize_inner()
if (arena)
thd->restore_active_arena(arena, &backup);
}
if (setup_jtbm_semi_joins(this, join_list, &conds))
List<Item> eq_list;
if (setup_degenerate_jtbm_semi_joins(this, join_list, eq_list))
DBUG_RETURN(1);
if (eq_list.elements != 0)
{
Item *new_cond;
if (eq_list.elements == 1)
new_cond= eq_list.pop();
else
new_cond= new (thd->mem_root) Item_cond_and(thd, eq_list);
if (new_cond &&
((new_cond->fix_fields(thd, &new_cond) ||
!(conds= and_items(thd, conds, new_cond)) ||
conds->fix_fields(thd, &conds))))
DBUG_RETURN(TRUE);
}
eq_list.empty();
if (select_lex->cond_pushed_into_where)
{
conds= and_conds(thd, conds, select_lex->cond_pushed_into_where);
@ -1641,6 +1660,32 @@ JOIN::optimize_inner()
conds= optimize_cond(this, conds, join_list, FALSE,
&cond_value, &cond_equal, OPT_LINK_EQUAL_FIELDS);
if (thd->lex->sql_command == SQLCOM_SELECT &&
optimizer_flag(thd, OPTIMIZER_SWITCH_COND_PUSHDOWN_FOR_SUBQUERY))
{
TABLE_LIST *tbl;
List_iterator_fast<TABLE_LIST> li(select_lex->leaf_tables);
while ((tbl= li++))
if (tbl->jtbm_subselect)
{
if (tbl->jtbm_subselect->pushdown_cond_for_in_subquery(thd, conds))
DBUG_RETURN(1);
}
}
if (setup_jtbm_semi_joins(this, join_list, eq_list))
DBUG_RETURN(1);
if (eq_list.elements != 0)
{
conds= and_new_conditions_to_optimized_cond(thd, conds, &cond_equal,
eq_list, &cond_value);
if (!conds &&
cond_value != Item::COND_FALSE && cond_value != Item::COND_TRUE)
DBUG_RETURN(TRUE);
}
if (thd->lex->sql_command == SQLCOM_SELECT &&
optimizer_flag(thd, OPTIMIZER_SWITCH_COND_PUSHDOWN_FOR_DERIVED))
{
@ -1679,7 +1724,6 @@ JOIN::optimize_inner()
if (select_lex->handle_derived(thd->lex, DT_OPTIMIZE))
DBUG_RETURN(1);
}
if (thd->is_error())
{
error= 1;
@ -13382,9 +13426,9 @@ finish:
FALSE otherwise
*/
static bool check_simple_equality(THD *thd, const Item::Context &ctx,
Item *left_item, Item *right_item,
COND_EQUAL *cond_equal)
bool check_simple_equality(THD *thd, const Item::Context &ctx,
Item *left_item, Item *right_item,
COND_EQUAL *cond_equal)
{
Item *orig_left_item= left_item;
Item *orig_right_item= right_item;