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If a join query uses a derived table (view / CTE) with GROUP BY clause then the execution plan for such join may employ split optimization. When this optimization is employed the derived table is not materialized. Rather only some partitions of the derived table are subject to grouping. Split optimization can be applied only if: - there are some indexes over the tables used in the join specifying the derived table whose prefixes partially cover the field items used in the GROUP BY list (such indexes are called splitting indexes) - the WHERE condition of the join query contains conjunctive equalities between columns of the derived table that comprise major parts of splitting indexes and columns of the other join tables. When the optimizer evaluates extending of a partial join by the rows of the derived table it always considers a possibility of using split optimization. Different splitting indexes can be used depending on the extended partial join. At some rare conditions, for example, when there is a non-splitting covering index for a table joined in the join specifying the derived table usage of a splitting index to produce rows needed for grouping may be still less beneficial than usage of such covering index without any splitting technique. The function JOIN_TAB::choose_best_splitting() must take this into account. Approved by Oleksandr Byelkin <sanja@mariadb.com>
237 lines
8.2 KiB
Text
237 lines
8.2 KiB
Text
#
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# MDEV-16917: do not use splitting for derived with join cache
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#
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CREATE TABLE t1 (
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n1 int(10) NOT NULL,
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n2 int(10) NOT NULL,
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c1 char(1) NOT NULL,
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KEY c1 (c1),
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KEY n1_c1_n2 (n1,c1,n2)
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) ENGINE=InnoDB;
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INSERT INTO t1 VALUES (0, 2, 'a'), (1, 3, 'a');
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ANALYZE TABLE t1;
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Table Op Msg_type Msg_text
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test.t1 analyze status OK
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EXPLAIN SELECT t1.n1 FROM t1, (SELECT n1, n2 FROM t1 WHERE c1 = 'a' GROUP BY n1) as t
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WHERE t.n1 = t1.n1 AND t.n2 = t1.n2 AND c1 = 'a' GROUP BY n1;
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id select_type table type possible_keys key key_len ref rows Extra
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1 PRIMARY t1 index c1,n1_c1_n2 n1_c1_n2 9 NULL 2 Using where; Using index
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1 PRIMARY <derived2> ref key0 key0 8 test.t1.n1,test.t1.n2 2
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2 LATERAL DERIVED t1 ref c1,n1_c1_n2 n1_c1_n2 4 test.t1.n1 1 Using where; Using index
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SELECT t1.n1 FROM t1, (SELECT n1, n2 FROM t1 WHERE c1 = 'a' GROUP BY n1) as t
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WHERE t.n1 = t1.n1 AND t.n2 = t1.n2 AND c1 = 'a' GROUP BY n1;
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n1
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0
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1
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DROP TABLE t1;
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#
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# MDEV-17211: splittable materialized derived joining 3 tables with
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# GROUP BY list containing fields from 2 of them
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#
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CREATE TABLE t1 (
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id1 int, i1 int, id2 int,
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PRIMARY KEY (id1), KEY (i1), KEY (id2)
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) ENGINE=InnoDB;
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INSERT INTO t1 VALUES (1,1,1);
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CREATE TABLE t2 (id2 int, i2 int) ENGINE=InnoDB;
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INSERT INTO t2 VALUES (1, 1);
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CREATE TABLE t3 (id3 int, i3 int, PRIMARY KEY (id3)) ENGINE=InnoDB;
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INSERT INTO t3 VALUES (1,1);
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EXPLAIN SELECT id3
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FROM (SELECT t3.id3, t2.i2, t1.id2 FROM t3,t1,t2
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WHERE t3.i3=t1.id1 AND t2.id2=t1.id2
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GROUP BY t3.id3, t1.id2) AS t,
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t2
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WHERE t2.id2=t.id2;
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id select_type table type possible_keys key key_len ref rows Extra
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1 PRIMARY t2 ALL NULL NULL NULL NULL 1 Using where
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1 PRIMARY <derived2> ref key0 key0 5 test.t2.id2 2
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2 DERIVED t3 ALL NULL NULL NULL NULL 1 Using where; Using temporary; Using filesort
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2 DERIVED t1 eq_ref PRIMARY,id2 PRIMARY 4 test.t3.i3 1
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2 DERIVED t2 ALL NULL NULL NULL NULL 1 Using where; Using join buffer (flat, BNL join)
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SELECT id3
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FROM (SELECT t3.id3, t2.i2, t1.id2 FROM t3,t1,t2
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WHERE t3.i3=t1.id1 AND t2.id2=t1.id2
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GROUP BY t3.id3, t1.id2) AS t,
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t2
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WHERE t2.id2=t.id2;
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id3
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1
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DROP TABLE t1,t2,t3;
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#
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# Bug mdev-17381: equi-join of derived table with join_cache_level=4
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#
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CREATE TABLE t1 (
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id int NOT NULL,
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amount decimal DEFAULT NULL,
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PRIMARY KEY (id)
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) ENGINE=INNODB;
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CREATE TABLE t2 (
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id int NOT NULL,
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name varchar(50) DEFAULT NULL,
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PRIMARY KEY (id)
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) ENGINE=INNODB;
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INSERT INTO t1 VALUES
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(1, 10.0000), (2, 20.0000), (3, 30.0000), (4, 40.0000),
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(5, NULL), (6, NULL), (7, 70.0000), (8, 80.0000);
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INSERT INTO t2 VALUES
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(1,'A'), (2,'B'), (3,'C'), (4,'D'), (5, NULL), (6, NULL),
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(7,'E'), (8,'F'), (9,'G'), (10,'H'), (11, NULL), (12, NULL);
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set join_cache_level=4;
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SELECT t2.id,t2.name,t.total_amt
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FROM t2
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LEFT JOIN
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(SELECT id, sum(amount) total_amt FROM t1 GROUP BY id) AS t
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ON t2.id=t.id
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WHERE t2.id < 3;
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id name total_amt
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1 A 10
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2 B 20
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EXPLAIN SELECT t2.id,t2.name,t.total_amt
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FROM t2
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LEFT JOIN
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(SELECT id, sum(amount) total_amt FROM t1 GROUP BY id) AS t
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ON t2.id=t.id
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WHERE t2.id < 3;
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id select_type table type possible_keys key key_len ref rows Extra
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1 PRIMARY t2 range PRIMARY PRIMARY 4 NULL 2 Using where
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1 PRIMARY <derived2> ref key0 key0 5 test.t2.id 2
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2 LATERAL DERIVED t1 eq_ref PRIMARY PRIMARY 4 test.t2.id 1
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set join_cache_level=default;
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DROP TABLE t1,t2;
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#
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# Bug mdev-18467: join of grouping view and a base table as inner operand
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# of left join with on condition containing impossible range
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#
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create table t1 (f1 int, f2 int, key(f2)) engine=InnoDB;
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insert into t1 values (3,33), (7,77), (1,11);
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create table t2 (f1 int, f2 int, primary key (f1)) engine=InnoDB;
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insert into t2 values (3,33), (9,99), (1,11);
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create view v1 as
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select f1, max(f2) as f2 from t2 group by f1;
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select t.f2
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from t1
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left join
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(v1 join t1 as t on v1.f1=t.f1 and t.f2 = null)
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on t1.f1=t.f1;
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f2
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NULL
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NULL
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NULL
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explain select t.f2
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from t1
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left join
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(v1 join t1 as t on v1.f1=t.f1 and t.f2 = null)
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on t1.f1=t.f1;
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id select_type table type possible_keys key key_len ref rows Extra
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1 PRIMARY t const f2 NULL NULL NULL 1 Impossible ON condition
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1 PRIMARY <derived2> const key1 NULL NULL NULL 1 Impossible ON condition
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1 PRIMARY t1 ALL NULL NULL NULL NULL 3
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2 DERIVED t2 ALL PRIMARY NULL NULL NULL 3 Using temporary; Using filesort
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set statement optimizer_switch='split_materialized=off' for explain select t.f2
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from t1
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left join
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(v1 join t1 as t on v1.f1=t.f1 and t.f2 = null)
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on t1.f1=t.f1;
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id select_type table type possible_keys key key_len ref rows Extra
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1 PRIMARY t const f2 NULL NULL NULL 1 Impossible ON condition
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1 PRIMARY <derived2> const key1 NULL NULL NULL 1 Impossible ON condition
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1 PRIMARY t1 ALL NULL NULL NULL NULL 3
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2 DERIVED t2 index NULL PRIMARY 4 NULL 3
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drop view v1;
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drop table t1,t2;
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#
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# MDEV-23723: Crash when test_if_skip_sort_order() is checked for derived table subject to split
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#
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CREATE TABLE t1 (a INT, b INT, KEY (a), KEY (a,b)) ENGINE=InnoDB;
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CREATE TABLE t2 (c INT, KEY (c)) ENGINE=InnoDB;
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SELECT * FROM t1 t1a JOIN t1 t1b;
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a b a b
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INSERT INTO t2 VALUES (1),(2);
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INSERT INTO t1 VALUES (1,2),(3,4),(5,6),(7,8),(9,10),(11,12);
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set statement optimizer_switch='split_materialized=off' for EXPLAIN
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SELECT *
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FROM
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t1 JOIN
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(SELECT t1.a, t1.b FROM t1, t2 WHERE t1.b = t2.c GROUP BY t1.a, t1.b) as dt
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WHERE
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t1.a = dt.a;
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id select_type table type possible_keys key key_len ref rows Extra
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1 PRIMARY t1 index a,a_2 a_2 10 NULL 6 Using where; Using index
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1 PRIMARY <derived2> ref key0 key0 5 test.t1.a 2
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2 DERIVED t1 index NULL a_2 10 NULL 6 Using where; Using index
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2 DERIVED t2 ref c c 5 test.t1.b 1 Using index
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set statement optimizer_switch='split_materialized=on' for EXPLAIN
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SELECT *
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FROM
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t1 JOIN
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(SELECT t1.a, t1.b FROM t1, t2 WHERE t1.b = t2.c GROUP BY t1.a, t1.b) as dt
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WHERE
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t1.a = dt.a;
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id select_type table type possible_keys key key_len ref rows Extra
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1 PRIMARY t1 index a,a_2 a_2 10 NULL 6 Using where; Using index
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1 PRIMARY <derived2> ref key0 key0 5 test.t1.a 2
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2 LATERAL DERIVED t1 ref a,a_2 a 5 test.t1.a 1 Using where; Using temporary; Using filesort
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2 LATERAL DERIVED t2 ref c c 5 test.t1.b 1 Using index
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DROP TABLE t1, t2;
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#
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# Bug mdev-25714: usage non-splitting covering index is cheaper than
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# usage of the best splitting index for one group
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#
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create table t1 (
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id int not null, itemid int not null, index idx (itemid)
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) engine=innodb;
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insert into t1 values (1, 2), (2,2), (4,2), (4,2), (0,3), (3,3);
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create table t2 (id int not null) engine=innodb;
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insert into t2 values (2);
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create table t3 (
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id int not null, itemid int not null, userid int not null, primary key (id),
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index idx1 (userid, itemid), index idx2 (itemid)
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) engine innodb;
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insert into t3 values (1,1,1), (2,1,1), (3,2,1), (4,2,1), (5,3,1);
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analyze table t1,t2,t3;
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Table Op Msg_type Msg_text
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test.t1 analyze status OK
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test.t2 analyze status OK
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test.t3 analyze status OK
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set optimizer_switch='split_materialized=on';
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explain select t1.id, t1.itemid, dt.id, t2.id
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from t1,
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(select itemid, max(id) as id from t3 where userid = 1 group by itemid) dt,
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t2
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where t1.id = dt.id and t1.itemid = dt.itemid and t2.id=t1.itemid;
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id select_type table type possible_keys key key_len ref rows Extra
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1 PRIMARY t2 ALL NULL NULL NULL NULL 1
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1 PRIMARY t1 ref idx idx 4 test.t2.id 1
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1 PRIMARY <derived2> ref key0 key0 9 test.t2.id,test.t1.id 2
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2 DERIVED t3 ref idx1,idx2 idx1 4 const 5 Using where; Using index
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select t1.id, t1.itemid, dt.id, t2.id
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from t1,
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(select itemid, max(id) as id from t3 where userid = 1 group by itemid) dt,
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t2
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where t1.id = dt.id and t1.itemid = dt.itemid and t2.id=t1.itemid;
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id itemid id id
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4 2 4 2
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4 2 4 2
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set optimizer_switch='split_materialized=off';
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explain select t1.id, t1.itemid, dt.id, t2.id
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from t1,
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(select itemid, max(id) as id from t3 where userid = 1 group by itemid) dt,
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t2
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where t1.id = dt.id and t1.itemid = dt.itemid and t2.id=t1.itemid;
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id select_type table type possible_keys key key_len ref rows Extra
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1 PRIMARY t2 ALL NULL NULL NULL NULL 1
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1 PRIMARY t1 ref idx idx 4 test.t2.id 1
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1 PRIMARY <derived2> ref key0 key0 9 test.t2.id,test.t1.id 2
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2 DERIVED t3 ref idx1 idx1 4 const 5 Using where; Using index
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select t1.id, t1.itemid, dt.id, t2.id
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from t1,
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(select itemid, max(id) as id from t3 where userid = 1 group by itemid) dt,
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t2
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where t1.id = dt.id and t1.itemid = dt.itemid and t2.id=t1.itemid;
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id itemid id id
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4 2 4 2
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4 2 4 2
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drop table t1,t2,t3;
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set optimizer_switch='split_materialized=default';
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# End of 10.3 tests
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