如何使好索引的MySQL表加入有效

Question

这是第一个表“TBL1”：

+---------+---------------------+------+-----+---------+----------------+ 
| Field | Type    | Null | Key | Default | Extra   | 
+---------+---------------------+------+-----+---------+----------------+ 
| val  | varchar(45)   | YES | MUL | NULL |    | 
| id  | bigint(20) unsigned | NO | PRI | NULL | auto_increment | 
+---------+---------------------+------+-----+---------+----------------+ 

凭借其索引：

+-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+ 
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | 
+-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+ 
| tbl1 |   0 | PRIMARY |   1 | id   | A   | 201826018 |  NULL | NULL |  | BTREE  |   | 
| tbl1 |   1 | val  |   1 | val   | A   |  2147085 |  NULL | NULL | YES | BTREE  |   | 
| tbl1 |   1 | id_val |   1 | id   | A   | 201826018 |  NULL | NULL |  | BTREE  |   | 
| tbl1 |   1 | id_val |   2 | val   | A   | 201826018 |  NULL | NULL | YES | BTREE  |   | 
| tbl1 |   1 | val_id |   1 | val   | A   |  2147085 |  NULL | NULL | YES | BTREE  |   | 
| tbl1 |   1 | val_id |   2 | id   | A   | 201826018 |  NULL | NULL |  | BTREE  |   | 
+-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+ 

（之所以一些额外的索引是这样的：http://bit.ly/KWx1Xz ）

第二张表大致相同。下面是它的索引基数虽：

+--------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+ 
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | 
+--------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+ 
| tbl2 |   0 | PRIMARY |   1 | id   | A   | 201826018 |  NULL | NULL |  | BTREE  |   | 
| tbl2 |   1 | val  |   1 | val   | A   |  881336 |  NULL | NULL | YES | BTREE  |   | 
| tbl2 |   1 | id_val |   1 | id   | A   | 201826018 |  NULL | NULL |  | BTREE  |   | 
| tbl2 |   1 | id_val |   2 | val   | A   | 201826018 |  NULL | NULL | YES | BTREE  |   | 
| tbl2 |   1 | val_id |   1 | val   | A   |  881336 |  NULL | NULL | YES | BTREE  |   | 
| tbl2 |   1 | val_id |   2 | id   | A   | 201826018 |  NULL | NULL |  | BTREE  |   | 
+--------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+ 

的任务是内加入他们的VAL列，并获得ID的列表（和做，在1秒）。

这里是 '加入' 的做法：

SELECT tbl1.id FROM tbl1 JOIN tbl2 ON tbl1.val = 'iii' AND tbl2.val = 'iii' AND tbl1.id = tbl2.id; 

结果：10831行中集（55.15秒）

查询说明：

+----+-------------+--------+--------+----------------------------------+---------+---------+---------------------------+------+--------------------------+ 
| id | select_type | table | type | possible_keys     | key  | key_len | ref      | rows | Extra     | 
+----+-------------+--------+--------+----------------------------------+---------+---------+---------------------------+------+--------------------------+ 
| 1 | SIMPLE  | tbl1 | ref | PRIMARY,val,id_val,val_id  | val_id | 138  | const      | 5160 | Using where; Using index | 
| 1 | SIMPLE  | tbl2 | eq_ref | PRIMARY,val,id_val,val_id  | PRIMARY | 8  | search_test.tbl1.id  | 1 | Using where    | 
+----+-------------+--------+--------+----------------------------------+---------+---------+---------------------------+------+--------------------------+ 

这里是' in'方法：

SELECT id FROM tbl1 WHERE val = 'iii' and id IN (SELECT id FROM tbl2 WHERE val = 'iii'); 

结果：10831行中集（1分10.15秒）

解释：

+----+--------------------+--------+-----------------+---------------------------------+---------+---------+-------+------+--------------------------+ 
| id | select_type  | table | type   | possible_keys     | key  | key_len | ref | rows | Extra     | 
+----+--------------------+--------+-----------------+---------------------------------+---------+---------+-------+------+--------------------------+ 
| 1 | PRIMARY   | tbl1 | ref    | val,val_id      | val_id | 138  | const | 8553 | Using where; Using index | 
| 2 | DEPENDENT SUBQUERY | tbl2 | unique_subquery | PRIMARY,val,id_val,val_id  | PRIMARY | 8  | func | 1 | Using where    | 
+----+--------------------+--------+-----------------+---------------------------------+---------+---------+-------+------+--------------------------+ 

所以，这里是一个问题：如何调整这个查询让MySQL的完成它在第二？

Answer 1

好的我已经在每张桌上30,000+条记录上进行了测试，它运行得非常快。

因为它目前为你表演上两个巨大的表联接现，但如果您扫描的比赛上“VAL”在每张桌子上：第一，将大大减少你的加入集的大小。

我最初把这个答案作为一组子查询发布，但是我没有意识到MySQL在嵌套子查询中的速度很慢，因为它从外部执行。但是，如果将子查询定义为视图，它会从内部出。

所以，先创建视图。

CREATE VIEW tbl1_iii AS (
SELECT * FROM tbl1 WHERE val='iii' 
); 
CREATE VIEW tbl2_iii AS (
SELECT * FROM tbl2 WHERE val='iii' 
); 

然后运行查询。

SELECT tbl1_iii.id from tbl1_iii,tbl2_iii 
WHERE tbl1_iii.id = tbl2_iii.id; 

闪电。

Answer 2

SELECT tbl1.id FROM tbl1 JOIN tbl2 ON tbl1.id = tbl2.id and tbl1.val = tbl2.val 
where tbl1.val = 'iii';