使用JOIN和GROUP BY优化的MySQL查询.可能吗？

Question

我有两个表:gpnxuser和key_value

mysql> describe gpnxuser;
+--------------+--------------+------+-----+---------+----------------+
| Field        | Type         | Null | Key | Default | Extra          |
+--------------+--------------+------+-----+---------+----------------+
| id           | bigint(20)   | NO   | PRI | NULL    | auto_increment |
| version      | bigint(20)   | NO   |     | NULL    |                |
| email        | varchar(255) | YES  |     | NULL    |                |
| uuid         | varchar(255) | NO   | MUL | NULL    |                |
| partner_id   | bigint(20)   | NO   | MUL | NULL    |                |
| password     | varchar(255) | YES  |     | NULL    |                |
| date_created | datetime     | YES  |     | NULL    |                |
| last_updated | datetime     | YES  |     | NULL    |                |
+--------------+--------------+------+-----+---------+----------------+

和

mysql> describe key_value;
+----------------+--------------+------+-----+---------+----------------+
| Field          | Type         | Null | Key | Default | Extra          |
+----------------+--------------+------+-----+---------+----------------+
| id             | bigint(20)   | NO   | PRI | NULL    | auto_increment |
| version        | bigint(20)   | NO   |     | NULL    |                |
| date_created   | datetime     | YES  |     | NULL    |                |
| last_updated   | datetime     | YES  |     | NULL    |                |
| upkey          | varchar(255) | NO   | MUL | NULL    |                |
| user_id        | bigint(20)   | YES  | MUL | NULL    |                |
| security_level | int(11)      | NO   |     | NULL    |                |
+----------------+--------------+------+-----+---------+----------------+

key_value.user_id是引用gpnxuser.id的FK.我在gpnxuser.partner_id中也有一个索引,它是一个引用名为"partner"的表的FK(我认为这对这个问题并不重要).

对于partner_id = 64,我在gpnxuser中有500K行,它与key_value中的大约6M行有关.

我希望有一个查询返回属于给定合作伙伴的用户的所有不同的'key_value.upkey'.我做了这样的事情:

select upkey from gpnxuser join key_value on gpnxuser.id=key_value.user_id where partner_id=64 group by upkey;

这需要永远运行.查询的解释如下:

mysql> explain select upkey from gpnxuser join key_value on gpnxuser.id=key_value.user_id where partner_id=64 group by upkey;

    +----+-------------+-----------+------+----------------------------+--------------------+---------+-----------------------------+--------+----------------------------------------------+
    | id | select_type | table     | type | possible_keys              | key                | key_len | ref                         | rows   | Extra                                        |
    +----+-------------+-----------+------+----------------------------+--------------------+---------+-----------------------------+--------+----------------------------------------------+
    |  1 | SIMPLE      | gpnxuser  | ref  | PRIMARY,FKB2D9FEBE725C505E | FKB2D9FEBE725C505E | 8       | const                       | 259640 | Using index; Using temporary; Using filesort |
    |  1 | SIMPLE      | key_value | ref  | FK9E0C0F912D11F5A9         | FK9E0C0F912D11F5A9 | 9       | gpnx_finance_db.gpnxuser.id |     14 | Using where                                  |
    +----+-------------+-----------+------+----------------------------+--------------------+---------+-----------------------------+--------+----------------------------------------------+

我的问题是:是否有一个可以快速运行并获得我想要的结果的查询？

Answer 1

您需要做的是利用EXISTS语句：这将仅导致部分表扫描，直到找到匹配项，而不是更多。

select upkey from (select distinct upkey from key_value) upk 
where EXISTS 
    (select 1 from gpnxuser u, key_value kv 
     where u.id=kv.user_id and partner_id=1 and kv.upkey = upk.upkey)

注意。在原始查询中，group by被误用：distinct看起来更好。

select DISTINCT upkey from gpnxuser join key_value on 
gpnxuser.id=key_value.user_id where partner_id=1