BUG#16393: Let the 'ref' optimizer use ON condition of nested join to construct (2956a79b) · Commits · Software / OSDI20 Artifacts / mariadb

mysql-test/r/join_nested.result

+17 −3

Original line number	Diff line number	Diff line
		@@ -960,7 +960,7 @@ id select_type table type possible_keys key key_len ref rows Extra
		1 SIMPLE t2 ALL NULL NULL NULL NULL 3 Using where
		1 SIMPLE t3 ALL NULL NULL NULL NULL 2 Using where
		1 SIMPLE t4 ref idx_b idx_b 5 test.t2.b 2 Using where
		1 SIMPLE t5 ALL NULL NULL NULL NULL 3 Using where
		1 SIMPLE t5 ALL idx_b NULL NULL NULL 3 Using where
		1 SIMPLE t7 ALL NULL NULL NULL NULL 2 Using where
		1 SIMPLE t6 ALL NULL NULL NULL NULL 3 Using where
		1 SIMPLE t8 ALL NULL NULL NULL NULL 2 Using where
		@@ -1009,7 +1009,7 @@ id select_type table type possible_keys key key_len ref rows Extra
		1 SIMPLE t2 ALL NULL NULL NULL NULL 3 Using where
		1 SIMPLE t3 ALL NULL NULL NULL NULL 2 Using where
		1 SIMPLE t4 ref idx_b idx_b 5 test.t2.b 2 Using where
		1 SIMPLE t5 ALL NULL NULL NULL NULL 3 Using where
		1 SIMPLE t5 ALL idx_b NULL NULL NULL 3 Using where
		1 SIMPLE t7 ALL NULL NULL NULL NULL 2 Using where
		1 SIMPLE t6 ALL NULL NULL NULL NULL 3 Using where
		1 SIMPLE t8 ref idx_b idx_b 5 test.t5.b 2 Using where
		@@ -1059,7 +1059,7 @@ id select_type table type possible_keys key key_len ref rows Extra
		1 SIMPLE t2 ALL NULL NULL NULL NULL 3 Using where
		1 SIMPLE t3 ALL NULL NULL NULL NULL 2 Using where
		1 SIMPLE t4 ref idx_b idx_b 5 test.t2.b 2 Using where
		1 SIMPLE t5 ALL NULL NULL NULL NULL 3 Using where
		1 SIMPLE t5 ALL idx_b NULL NULL NULL 3 Using where
		1 SIMPLE t7 ALL NULL NULL NULL NULL 2 Using where
		1 SIMPLE t6 ALL NULL NULL NULL NULL 3 Using where
		1 SIMPLE t8 ref idx_b idx_b 5 test.t5.b 2 Using where
		@@ -1467,3 +1467,17 @@ id select_type table type possible_keys key key_len ref rows Extra
		1 SIMPLE t6 ref a a 5 test.t4.b X
		1 SIMPLE t5 ref a a 5 test.t3.b X
		drop table t0, t1, t2, t3, t4, t5, t6, t7;
		create table t1 (a int);
		insert into t1 values (0),(1),(2),(3),(4),(5),(6),(7),(8),(9);
		create table t2 (a int, filler char(100), key(a));
		insert into t2 select A.a + 10*B.a, '' from t1 A, t1 B;
		create table t3 like t2;
		insert into t3 select * from t2;
		explain select * from t1 left join
		(t2 left join t3 on (t2.a = t3.a))
		on (t1.a = t2.a);
		id select_type table type possible_keys key key_len ref rows Extra
		1 SIMPLE t1 ALL NULL NULL NULL NULL 10
		1 SIMPLE t2 ref a a 5 test.t1.a 1
		1 SIMPLE t3 ref a a 5 test.t2.a 1
		drop table t1, t2, t3;

mysql-test/t/join_nested.test

+14 −0

Original line number	Diff line number	Diff line
		@@ -900,3 +900,17 @@ explain select * from t2 left join
		join t5 on t5.a=t3.b) on t3.a=t2.b;

		drop table t0, t1, t2, t3, t4, t5, t6, t7;

		# BUG#16393
		create table t1 (a int);
		insert into t1 values (0),(1),(2),(3),(4),(5),(6),(7),(8),(9);
		create table t2 (a int, filler char(100), key(a));
		insert into t2 select A.a + 10*B.a, '' from t1 A, t1 B;
		create table t3 like t2;
		insert into t3 select * from t2;

		explain select * from t1 left join
		(t2 left join t3 on (t2.a = t3.a))
		on (t1.a = t2.a);
		drop table t1, t2, t3;

sql/sql_select.cc

+68 −12

Original line number	Diff line number	Diff line
		@@ -2917,6 +2917,64 @@ sort_keyuse(KEYUSE a,KEYUSE b)
		}


		/*
		Add to KEY_FIELD array all 'ref' access candidates within nested join

		SYNPOSIS
		add_key_fields_for_nj()
		nested_join_table IN Nested join pseudo-table to process
		end INOUT End of the key field array
		and_level INOUT And-level

		DESCRIPTION
		This function populates KEY_FIELD array with entries generated from the
		ON condition of the given nested join, and does the same for nested joins
		contained within this nested join.

		IMPLEMENTATION
		We can add accesses to the tables that are direct children of this nested
		join (1), and are not inner tables w.r.t their neighbours (2).

		Example for #1 (outer brackets pair denotes nested join this function is
		invoked for):

		... LEFT JOIN (t1 LEFT JOIN (t2 ... ) ) ON cond

		Example for #2:

		... LEFT JOIN (t1 LEFT JOIN t2 ) ON cond

		In examples 1-2 for condition cond, we can add 'ref' access candidates to
		t1 only.

		Example #3:

		... LEFT JOIN (t1, t2 JOIN t3 ON inner_cond) ON cond

		Here we can add 'ref' access candidates for t1 and t2, but not for t3.

		*/

		static void add_key_fields_for_nj(TABLE_LIST *nested_join_table,
		KEY_FIELD *end, uint and_level)
		{
		List_iterator<TABLE_LIST> li(nested_join_table->nested_join->join_list);
		table_map tables= 0;
		TABLE_LIST *table;
		DBUG_ASSERT(nested_join_table->nested_join);

		while ((table= li++))
		{
		if (table->nested_join)
		add_key_fields_for_nj(table, end, and_level);
		else
		if (!table->on_expr)
		tables \|= table->table->map;
		}
		add_key_fields(end, and_level, nested_join_table->on_expr, tables);
		}


		/*
		Update keyuse array with all possible keys we can use to fetch rows

		@@ -2981,23 +3039,21 @@ update_ref_and_keys(THD thd, DYNAMIC_ARRAY keyuse,JOIN_TAB *join_tab,
		into account as well.
		*/
		if (*join_tab[i].on_expr_ref)
		{
		add_key_fields(&end,&and_level,*join_tab[i].on_expr_ref,
		join_tab[i].table->map);
		}
		else

		/* Process ON conditions for the nested joins */
		{
		TABLE_LIST *tab= join_tab[i].table->pos_in_table_list;
		TABLE_LIST *embedding= tab->embedding;
		if (embedding)
		List_iterator<TABLE_LIST> li(*join_tab->join->join_list);
		TABLE_LIST *table;
		while ((table= li++))
		{
		NESTED_JOIN *nested_join= embedding->nested_join;
		if (nested_join->join_list.head() == tab)
		add_key_fields(&end, &and_level, embedding->on_expr,
		nested_join->used_tables);
		}
		if (table->nested_join)
		add_key_fields_for_nj(table, &end, &and_level);
		}
		}

		/* fill keyuse with found key parts */
		for ( ; field != end ; field++)
		add_key_part(keyuse,field);