我想知道如何优化它，最好不要更改表格结构。
SELECT p.author_id member_id,
m.members_display_name member_name,
COUNT(p.pid) posts
FROM forum_topics t
STRAIGHT_JOIN forum_posts p
STRAIGHT_JOIN forum_members m
WHERE p.author_id != 0
AND p.author_id = m.member_id
AND p.new_topic = 0
AND t.forum_id = 120
AND t.tid = p.topic_id
GROUP BY p.author_id
ORDER BY posts DESC
LIMIT 1
EXPLAIN的输出是：
-------------------------------------------------------------------------------
EXPLAIN
SELECT p.author_id member_id,
m.members_display_name member_name,
COUNT(p.pid) posts
FROM forum_topics t
STRAIGHT_JOIN forum_posts p
STRAIGHT_JOIN forum_members m
WHERE p.author_id != 0
AND p.author_id = m.member_id
AND p.new_topic = 0
AND t.forum_id = 120
AND t.tid = p.topic_id
GROUP BY p.author_id
ORDER BY posts DESC
LIMIT 1\G
*************************** 1. row ***************************
id: 1
select_type: SIMPLE
table: t
type: ref
possible_keys: PRIMARY,forum_id,last_post
key: forum_id
key_len: 2
ref: const
rows: 28070
Extra: Using temporary; Using filesort
*************************** 2. row ***************************
id: 1
select_type: SIMPLE
table: p
type: ref
possible_keys: author_id,topic_id
key: topic_id
key_len: 4
ref: forumwmo.t.tid
rows: 5
Extra: Using where
*************************** 3. row ***************************
id: 1
select_type: SIMPLE
table: m
type: eq_ref
possible_keys: PRIMARY
key: PRIMARY
key_len: 3
ref: forumwmo.p.author_id
rows: 1
Extra:
3 rows in set (0.00 sec)
表结构是：
SHOW CREATE TABLE forum_members\G
*************************** 1. row ***************************
Table: forum_members
Create Table: CREATE TABLE `forum_members` (
`member_id` mediumint(8) NOT NULL AUTO_INCREMENT,
`name` varchar(32) NOT NULL DEFAULT '',
`member_group_id` smallint(3) NOT NULL DEFAULT '0',
`email` varchar(150) NOT NULL DEFAULT '',
`joined` int(10) NOT NULL DEFAULT '0',
`ip_address` varchar(16) NOT NULL DEFAULT '',
`posts` mediumint(7) DEFAULT '0',
`title` varchar(64) DEFAULT NULL,
`allow_admin_mails` tinyint(1) DEFAULT NULL,
`time_offset` varchar(10) DEFAULT NULL,
`hide_email` varchar(8) DEFAULT NULL,
`email_pm` tinyint(1) DEFAULT NULL,
`email_full` tinyint(1) DEFAULT NULL,
`skin` smallint(5) DEFAULT NULL,
`warn_level` int(10) DEFAULT NULL,
`warn_lastwarn` int(10) NOT NULL DEFAULT '0',
`language` varchar(32) DEFAULT NULL,
`last_post` int(10) DEFAULT NULL,
`restrict_post` varchar(100) NOT NULL DEFAULT '0',
`view_sigs` tinyint(1) DEFAULT '1',
`view_img` tinyint(1) DEFAULT '1',
`view_avs` tinyint(1) DEFAULT '1',
`view_pop` tinyint(1) DEFAULT '1',
`bday_day` int(2) DEFAULT NULL,
`bday_month` int(2) DEFAULT NULL,
`bday_year` int(4) DEFAULT NULL,
`msg_count_new` int(2) NOT NULL DEFAULT '0',
`msg_count_total` int(3) NOT NULL DEFAULT '0',
`msg_count_reset` int(1) NOT NULL DEFAULT '0',
`msg_show_notification` int(1) NOT NULL DEFAULT '0',
`misc` varchar(128) DEFAULT NULL,
`last_visit` int(10) DEFAULT '0',
`last_activity` int(10) DEFAULT '0',
`dst_in_use` tinyint(1) DEFAULT '0',
`view_prefs` varchar(64) DEFAULT '-1&-1',
`coppa_user` tinyint(1) DEFAULT '0',
`mod_posts` varchar(100) NOT NULL DEFAULT '0',
`auto_track` varchar(50) DEFAULT '0',
`org_perm_id` varchar(255) DEFAULT '',
`temp_ban` varchar(100) DEFAULT '0',
`sub_end` int(10) NOT NULL DEFAULT '0',
`no_sig_lims` tinyint(1) NOT NULL DEFAULT '0',
`login_anonymous` char(3) NOT NULL DEFAULT '0&0',
`ignored_users` text,
`mgroup_others` varchar(255) NOT NULL DEFAULT '',
`member_login_key` varchar(32) NOT NULL DEFAULT '',
`member_login_key_expire` int(10) NOT NULL DEFAULT '0',
`subs_pkg_chosen` smallint(3) NOT NULL DEFAULT '0',
`has_blog` tinyint(1) NOT NULL DEFAULT '0',
`members_auto_dst` tinyint(1) NOT NULL DEFAULT '1',
`members_cache` mediumtext,
`members_disable_pm` int(1) NOT NULL DEFAULT '0',
`members_display_name` varchar(255) NOT NULL DEFAULT '',
`members_seo_name` varchar(255) NOT NULL DEFAULT '',
`members_created_remote` tinyint(1) NOT NULL DEFAULT '0',
`members_editor_choice` char(3) NOT NULL DEFAULT 'std',
`members_profile_views` int(10) unsigned NOT NULL DEFAULT '0',
`members_l_display_name` varchar(255) NOT NULL DEFAULT '0',
`members_l_username` varchar(255) NOT NULL DEFAULT '0',
`failed_logins` text,
`failed_login_count` smallint(3) NOT NULL DEFAULT '0',
`has_gallery` int(1) DEFAULT '0',
`members_pass_hash` varchar(32) NOT NULL DEFAULT '',
`members_pass_salt` varchar(5) NOT NULL DEFAULT '',
`member_banned` tinyint(1) NOT NULL DEFAULT '0',
`identity_url` text,
`member_uploader` varchar(32) NOT NULL DEFAULT 'default',
`members_bitoptions` int(10) unsigned NOT NULL DEFAULT '0',
`fb_uid` bigint(20) NOT NULL DEFAULT '0',
`fb_emailhash` varchar(60) NOT NULL DEFAULT '',
`fb_emailallow` int(1) NOT NULL DEFAULT '0',
`fb_lastsync` int(10) NOT NULL DEFAULT '0',
`members_day_posts` varchar(32) NOT NULL DEFAULT '0,0',
`live_id` varchar(32) DEFAULT NULL,
PRIMARY KEY (`member_id`),
KEY `mgroup` (`member_group_id`),
KEY `bday_day` (`bday_day`),
KEY `bday_month` (`bday_month`),
KEY `members_l_display_name` (`members_l_display_name`),
KEY `members_l_username` (`members_l_username`),
KEY `member_banned` (`member_banned`),
KEY `members_bitoptions` (`members_bitoptions`),
KEY `ip_address` (`ip_address`)
) ENGINE=MyISAM AUTO_INCREMENT=101965 DEFAULT CHARSET=latin1
1 row in set (0.00 sec)
-------------------------------------------------------------------------------
SHOW CREATE TABLE forum_posts\G
*************************** 1. row ***************************
Table: forum_posts
Create Table: CREATE TABLE `forum_posts` (
`append_edit` tinyint(1) DEFAULT '0',
`edit_time` int(10) DEFAULT NULL,
`pid` int(10) NOT NULL AUTO_INCREMENT,
`author_id` mediumint(8) NOT NULL DEFAULT '0',
`author_name` varchar(32) DEFAULT NULL,
`use_sig` tinyint(1) NOT NULL DEFAULT '0',
`use_emo` tinyint(1) NOT NULL DEFAULT '0',
`ip_address` varchar(16) NOT NULL DEFAULT '',
`post_date` int(10) DEFAULT NULL,
`icon_id` smallint(3) DEFAULT NULL,
`post` mediumtext,
`queued` tinyint(1) NOT NULL DEFAULT '0',
`topic_id` int(10) NOT NULL DEFAULT '0',
`post_title` varchar(255) DEFAULT NULL,
`new_topic` tinyint(1) DEFAULT '0',
`edit_name` varchar(255) DEFAULT NULL,
`post_parent` int(10) NOT NULL DEFAULT '0',
`post_key` varchar(32) NOT NULL DEFAULT '0',
`post_htmlstate` smallint(1) NOT NULL DEFAULT '0',
`post_edit_reason` varchar(255) NOT NULL DEFAULT '',
PRIMARY KEY (`pid`),
KEY `author_id` (`author_id`,`topic_id`),
KEY `post_date` (`post_date`),
KEY `topic_id` (`topic_id`,`queued`,`pid`,`post_date`),
KEY `post_key` (`post_key`),
KEY `ip_address` (`ip_address`)
) ENGINE=MyISAM AUTO_INCREMENT=988489 DEFAULT CHARSET=latin1
1 row in set (0.00 sec)
-------------------------------------------------------------------------------
SHOW CREATE TABLE forum_topics\G
*************************** 1. row ***************************
Table: forum_topics
Create Table: CREATE TABLE `forum_topics` (
`tid` int(10) NOT NULL AUTO_INCREMENT,
`title` varchar(70) NOT NULL DEFAULT '',
`description` varchar(250) DEFAULT NULL,
`state` varchar(8) DEFAULT NULL,
`posts` int(10) DEFAULT NULL,
`starter_id` mediumint(8) NOT NULL DEFAULT '0',
`start_date` int(10) DEFAULT NULL,
`last_poster_id` mediumint(8) NOT NULL DEFAULT '0',
`last_post` int(10) DEFAULT NULL,
`icon_id` tinyint(2) DEFAULT NULL,
`starter_name` varchar(255) DEFAULT NULL,
`last_poster_name` varchar(255) DEFAULT NULL,
`poll_state` varchar(8) DEFAULT NULL,
`last_vote` int(10) DEFAULT NULL,
`views` int(10) DEFAULT '0',
`forum_id` smallint(5) NOT NULL DEFAULT '0',
`approved` tinyint(1) NOT NULL DEFAULT '0',
`author_mode` tinyint(1) DEFAULT NULL,
`pinned` tinyint(1) NOT NULL DEFAULT '0',
`moved_to` varchar(64) DEFAULT NULL,
`total_votes` int(5) NOT NULL DEFAULT '0',
`topic_hasattach` smallint(5) NOT NULL DEFAULT '0',
`topic_firstpost` int(10) NOT NULL DEFAULT '0',
`topic_queuedposts` int(10) NOT NULL DEFAULT '0',
`topic_rating_total` smallint(5) unsigned NOT NULL DEFAULT '0',
`topic_rating_hits` smallint(5) unsigned NOT NULL DEFAULT '0',
`topic_open_time` int(10) NOT NULL DEFAULT '0',
`topic_close_time` int(10) NOT NULL DEFAULT '0',
`title_seo` varchar(250) NOT NULL DEFAULT '',
`seo_last_name` varchar(255) NOT NULL DEFAULT '',
`seo_first_name` varchar(255) NOT NULL DEFAULT '',
PRIMARY KEY (`tid`),
KEY `topic_firstpost` (`topic_firstpost`),
KEY `forum_id` (`forum_id`,`pinned`,`approved`),
KEY `last_post` (`forum_id`,`pinned`,`last_post`),
KEY `starter_id` (`starter_id`,`forum_id`,`approved`),
KEY `last_post_sorting` (`last_post`,`forum_id`),
KEY `start_date` (`start_date`),
FULLTEXT KEY `title` (`title`)
) ENGINE=MyISAM AUTO_INCREMENT=227233 DEFAULT CHARSET=latin1
1 row in set (0.00 sec)
表格属性为：
SHOW TABLE STATUS LIKE 'forum_members'\G
*************************** 1. row ***************************
Name: forum_members
Engine: MyISAM
Version: 10
Row_format: Dynamic
Rows: 64866
Avg_row_length: 257
Data_length: 16688164
Max_data_length: 281474976710655
Index_length: 6540288
Data_free: 0
Auto_increment: 101965
Create_time: 2009-12-02 05:45:59
Update_time: 2009-12-02 05:46:07
Check_time: 2009-12-02 05:49:23
Collation: latin1_swedish_ci
Checksum: NULL
Create_options:
Comment:
1 row in set (0.00 sec)
-------------------------------------------------------------------------------
SHOW TABLE STATUS LIKE 'forum_posts'\G
*************************** 1. row ***************************
Name: forum_posts
Engine: MyISAM
Version: 10
Row_format: Dynamic
Rows: 581777
Avg_row_length: 720
Data_length: 419170168
Max_data_length: 281474976710655
Index_length: 46439424
Data_free: 0
Auto_increment: 988489
Create_time: 2009-12-02 05:47:04
Update_time: 2009-12-02 05:48:13
Check_time: 2009-12-02 05:49:28
Collation: latin1_swedish_ci
Checksum: NULL
Create_options:
Comment:
1 row in set (0.00 sec)
-------------------------------------------------------------------------------
SHOW TABLE STATUS LIKE 'forum_topics'\G
*************************** 1. row ***************************
Name: forum_topics
Engine: MyISAM
Version: 10
Row_format: Dynamic
Rows: 117458
Avg_row_length: 144
Data_length: 17004836
Max_data_length: 281474976710655
Index_length: 14105600
Data_free: 0
Auto_increment: 227233
Create_time: 2009-12-02 05:48:38
Update_time: 2009-12-02 05:48:43
Check_time: 2009-12-02 05:49:28
Collation: latin1_swedish_ci
Checksum: NULL
Create_options:
Comment:
1 row in set (0.00 sec)
其他配置详情：
SHOW VARIABLES LIKE '%buffer%'\G
*************************** 1. row ***************************
Variable_name: bulk_insert_buffer_size
Value: 8388608
*************************** 2. row ***************************
Variable_name: innodb_buffer_pool_size
Value: 8388608
*************************** 3. row ***************************
Variable_name: innodb_log_buffer_size
Value: 1048576
*************************** 4. row ***************************
Variable_name: join_buffer_size
Value: 131072
*************************** 5. row ***************************
Variable_name: key_buffer_size
Value: 8384512
*************************** 6. row ***************************
Variable_name: myisam_sort_buffer_size
Value: 8388608
*************************** 7. row ***************************
Variable_name: net_buffer_length
Value: 16384
*************************** 8. row ***************************
Variable_name: pbxt_log_buffer_size
Value: 256K
*************************** 9. row ***************************
Variable_name: pbxt_transaction_buffer_size
Value: 1MB
*************************** 10. row ***************************
Variable_name: preload_buffer_size
Value: 32768
*************************** 11. row ***************************
Variable_name: read_buffer_size
Value: 131072
*************************** 12. row ***************************
Variable_name: read_rnd_buffer_size
Value: 262144
*************************** 13. row ***************************
Variable_name: sort_buffer_size
Value: 2097144
*************************** 14. row ***************************
Variable_name: sql_buffer_result
Value: OFF
14 rows in set (0.00 sec)
答案 0 :(得分：1)
通过将一些WHERE子句条件移动到JOIN中，可能会提高性能，因为这会在执行查询时减少结果集，例如。
SELECT p.author_id member_id,
m.members_display_name member_name,
COUNT(p.pid) posts
FROM forum_topics t
STRAIGHT_JOIN forum_posts p
ON t.tid = p.topic_id
AND t.forum_id = 120
AND p.new_topic = 0
STRAIGHT_JOIN forum_members m
ON p.author_id = m.member_id
WHERE p.author_id != 0
GROUP BY p.author_id
ORDER BY posts DESC
LIMIT 1
虽然，优化器可能足够聪明，可以为您完成此操作。此外，虽然我不使用MySQL，但我对STRAIGH_JOIN的理解是它以明确的从左到右的顺序连接表，因此如果表按大小顺序从最小到最大列出，反之亦然，它可能会有所不同。