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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

18
sql/sql_select.h
View File

@ -1470,6 +1470,11 @@ public:
Dynamic_array<KEYUSE_EXT> *ext_keyuses_for_splitting;
JOIN_TAB *sort_and_group_aggr_tab;
/*
Flag is set to true if select_lex was found to be degenerated before
the optimize_cond() call in JOIN::optimize_inner() method.
*/
bool is_orig_degenerated;
JOIN(THD *thd_arg, List<Item> &fields_arg, ulonglong select_options_arg,
select_result *result_arg)
@ -1564,6 +1569,7 @@ public:
emb_sjm_nest= NULL;
sjm_lookup_tables= 0;
sjm_scan_tables= 0;
is_orig_degenerated= false;
}
/* True if the plan guarantees that it will be returned zero or one row */
@ -1734,6 +1740,7 @@ public:
bool fix_all_splittings_in_plan();
bool transform_in_predicates_into_in_subq(THD *thd);
bool add_equalities_to_where_condition(THD *thd, List<Item> &eq_list);
private:
/**
Create a temporary table to be used for processing DISTINCT/ORDER
@ -2325,7 +2332,7 @@ Item_equal *find_item_equal(COND_EQUAL *cond_equal, Field *field,
extern bool test_if_ref(Item *,
Item_field *left_item,Item *right_item);
inline bool optimizer_flag(THD *thd, uint flag)
inline bool optimizer_flag(THD *thd, ulonglong flag)
{
return (thd->variables.optimizer_switch & flag);
}
@ -2440,4 +2447,13 @@ int create_sort_index(THD *thd, JOIN *join, JOIN_TAB *tab, Filesort *fsort);
JOIN_TAB *first_explain_order_tab(JOIN* join);
JOIN_TAB *next_explain_order_tab(JOIN* join, JOIN_TAB* tab);
bool check_simple_equality(THD *thd, const Item::Context &ctx,
Item *left_item, Item *right_item,
COND_EQUAL *cond_equal);
void propagate_new_equalities(THD *thd, Item *cond,
List<Item_equal> *new_equalities,
COND_EQUAL *inherited,
bool *is_simplifiable_cond);
#endif /* SQL_SELECT_INCLUDED */