MySQL materialize optimiztion 还在整理中，未完善

测试环境

mysql> select version();
+-----------+
| version() |
+-----------+
| 5.6.36    |
+-----------+
1 row in set (0.00 sec)

 在两表没有任何索引和主键的情况下，MySQL默认选择Maerialized optimization，执行时间为0.41s

mysql> explain 
    -> select * from dbs t01
    -> where t01.dbid in 
    ->   ( select dbid from jbs t02 where id > 100 and id < 1000);
+----+--------------+-------------+--------+---------------+------------+---------+----------------------+--------+-------------+
| id | select_type  | table       | type   | possible_keys | key        | key_len | ref                  | rows   | Extra       |
+----+--------------+-------------+--------+---------------+------------+---------+----------------------+--------+-------------+
|  1 | SIMPLE       | t01         | ALL    | NULL          | NULL       | NULL    | NULL                 | 144411 | Using where |
|  1 | SIMPLE       | <subquery2> | eq_ref | <auto_key>    | <auto_key> | 8       | oracle_info.t01.DBID |      1 | NULL        |
|  2 | MATERIALIZED | t02         | ALL    | NULL          | NULL       | NULL    | NULL                 | 179525 | Using where |
+----+--------------+-------------+--------+---------------+------------+---------+----------------------+--------+-------------+
3 rows in set (0.00 sec)
mysql> select count(*) from dbs;
+----------+
| count(*) |
+----------+
|   145728 |
+----------+
1 row in set (0.07 sec)

mysql> select count(*) from jbs;
+----------+
| count(*) |
+----------+
|   186368 |
+----------+
1 row in set (0.08 sec)

执行过程：
1.创建基于jbs的临时表，并创建相应的索引id or dbid
2.用临时表和dbs表连接查询获得最后的结果

当MySQL没有有效索引的时候，MySQL materialization 会帮助优化器创建拥有索引的临时表提高MySQL查询引擎的执行效率

现在对jbs表id增加主键约束，测试执行结果时间为：0.38s

mysql> alter table jbs add primary key(id);
Query OK, 0 rows affected (5.04 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> explain  select * from dbs t01 where t01.dbid in    ( select dbid from jbs t02 where id > 100 and id < 1000);
+----+--------------+-------------+-------+---------------+---------+---------+------+--------+----------------------------------------------------+
| id | select_type  | table       | type  | possible_keys | key     | key_len | ref  | rows   | Extra                                              |
+----+--------------+-------------+-------+---------------+---------+---------+------+--------+----------------------------------------------------+
|  1 | SIMPLE       | <subquery2> | ALL   | NULL          | NULL    | NULL    | NULL |   NULL | NULL                                               |
|  1 | SIMPLE       | t01         | ALL   | NULL          | NULL    | NULL    | NULL | 144411 | Using where; Using join buffer (Block Nested Loop) |
|  2 | MATERIALIZED | t02         | range | PRIMARY       | PRIMARY | 4       | NULL |    213 | Using where                                        |
+----+--------------+-------------+-------+---------------+---------+---------+------+--------+----------------------------------------------------+
3 rows in set (0.00 sec)

 对表jbs、dbs列dbid增加索引，测试结果如下：

mysql> create index idx_01 on dbs(dbid);
Query OK, 0 rows affected (0.53 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> create index idx_02 on jbs(dbid);
Query OK, 0 rows affected (0.88 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> explain  select * from dbs t01 where t01.dbid in    ( select dbid from jbs t02 where id > 100 and id < 1000);
+----+--------------+-------------+--------+----------------+------------+---------+----------------------+--------+-------------+
| id | select_type  | table       | type   | possible_keys  | key        | key_len | ref                  | rows   | Extra       |
+----+--------------+-------------+--------+----------------+------------+---------+----------------------+--------+-------------+
|  1 | SIMPLE       | t01         | ALL    | idx_01         | NULL       | NULL    | NULL                 | 144411 | Using where |
|  1 | SIMPLE       | <subquery2> | eq_ref | <auto_key>     | <auto_key> | 8       | oracle_info.t01.DBID |      1 | NULL        |
|  2 | MATERIALIZED | t02         | range  | PRIMARY,idx_02 | PRIMARY    | 4       | NULL                 |    213 | Using where |
+----+--------------+-------------+--------+----------------+------------+---------+----------------------+--------+-------------+
3 rows in set (0.00 sec)

execution time 0.29s

优化器参数配置如下：

mysql> select @@optimizer_switch G
*************************** 1. row ***************************
@@optimizer_switch: index_merge=on,index_merge_union=on,index_merge_sort_union=on,index_merge_intersection=on,engine_condition_pushdown=on,index_condition_pushdown=on,mrr=on,mrr_cost_based=on,block_nested_loop=on,batched_key_access=off,materialization=on,semijoin=on,loosescan=on,firstmatch=on,subquery_materialization_cost_based=on,use_index_extensions=on

 修改优化器获得如下效果：

mysql> set optimizer_switch = 'index_merge=off,index_merge_union=off,index_merge_sort_union=off,index_merge_intersection=off,engine_condition_pushdown=off,index_condition_pushdown=off,mrr=off,mrr_cost_based=off,block_nested_loop=off,batched_key_access=off,materialization=off,semijoin=on,loosescan=on,firstmatch=on,subquery_materialization_cost_based=off,use_index_extensions=off';
Query OK, 0 rows affected (0.00 sec)

mysql> explain  select * from dbs t01 where t01.dbid in    ( select dbid from jbs t02 where id > 100 and id < 1000);                         +----+-------------+-------+-------+----------------+--------+---------+----------------------+--------+-------------------------------------+
| id | select_type | table | type  | possible_keys  | key    | key_len | ref                  | rows   | Extra                               |
+----+-------------+-------+-------+----------------+--------+---------+----------------------+--------+-------------------------------------+
|  1 | SIMPLE      | t02   | index | PRIMARY,idx_02 | idx_02 | 8       | NULL                 | 184904 | Using where; Using index; LooseScan |
|  1 | SIMPLE      | t01   | ref   | idx_01         | idx_01 | 8       | oracle_info.t02.dbid |   3282 | NULL                                |
+----+-------------+-------+-------+----------------+--------+---------+----------------------+--------+-------------------------------------+
2 rows in set (0.00 sec)

execution 0.38s

 删除两表的索引，获得如下结果：

mysql> drop index idx_01 on dbs;
Query OK, 0 rows affected (0.15 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> drop index idx_02 on jbs;
Query OK, 0 rows affected (0.13 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> explain  select * from dbs t01 where t01.dbid in    ( select dbid from jbs t02 where id > 100 and id < 1000);
+----+-------------+-------+-------+---------------+---------+---------+------+--------+------------------------------+
| id | select_type | table | type  | possible_keys | key     | key_len | ref  | rows   | Extra                        |
+----+-------------+-------+-------+---------------+---------+---------+------+--------+------------------------------+
|  1 | SIMPLE      | t02   | range | PRIMARY       | PRIMARY | 4       | NULL |    213 | Using where; Start temporary |
|  1 | SIMPLE      | t01   | ALL   | NULL          | NULL    | NULL    | NULL | 144411 | Using where; End temporary   |
+----+-------------+-------+-------+---------------+---------+---------+------+--------+------------------------------+
2 rows in set (0.00 sec)

execution time 33s
mysql> select @@optimizer_switch G
*************************** 1. row ***************************
@@optimizer_switch: index_merge=off,index_merge_union=off,index_merge_sort_union=off,index_merge_intersection=off,engine_condition_pushdown=off,index_condition_pushdown=off,mrr=off,mrr_cost_based=off,block_nested_loop=off,batched_key_access=off,materialization=off,semijoin=on,loosescan=on,firstmatch=on,subquery_materialization_cost_based=off,use_index_extensions=off

对比第一次执行，matierialization执行方式效率更好。