我有一个疑问:
SELECT *
FROM amp_ads,amp_c,amp_c_countries
WHERE
(amp_c.zone = '24' OR amp_c.zone = '25') AND
amp_ads.ad_complete = '1' AND
amp_ads.ad_type = '17' AND
amp_ads.accept = '1' AND
amp_ads.en_w = '1' AND
amp_c.en_u = '1' AND
amp_c.en_w = '1' AND
(amp_c.i_nu>'0' OR amp_c.c_nu>'0' OR amp_c.d_valid_by>'1299341823' OR amp_c.unlimit='1') AND
(amp_c.i_d_max='0' OR amp_c.i_d_nu>'0') AND
(amp_c.c_d_max='0' OR amp_c.c_d_nu>'0') AND
amp_c.t1<'1299341823' AND
amp_c.t2>'1299341823' AND
amp_c.d7 = '1' AND
(amp_c.some_countr = '0' OR (amp_c_countries.country = 'ES' AND amp_c.n = amp_c_countries.ad AND amp_c.camp = amp_c_countries.c)) AND
amp_c.n = amp_ads.n AND
amp_ads.def = 0
ORDER BY amp_c.price_c desc LIMIT 1
(实际上并非如此SELECT *
,但我简化了该SELECT
条款以使其不那么混乱。)
EXPLAIN
上述查询的输出是:
*************************** 1. row ***************************
id: 1
select_type: SIMPLE
table: amp_c
type: ref
possible_keys: work,n_index,zone_price
key: zone_price
key_len: 4
ref: const
rows: 79
Extra: Using where; Using temporary; Using filesort
*************************** 2. row ***************************
id: 1
select_type: SIMPLE
table: amp_ads
type: eq_ref
possible_keys: n,work
key: n
key_len: 4
ref: advertis_admpro.amp_c.n
rows: 1
Extra: Using where
*************************** 3. row ***************************
id: 1
select_type: SIMPLE
table: amp_c_countries
type: index
possible_keys: work
key: work
key_len: 12
ref: NULL
rows: 4083
Extra: Using where; Using index; Using join buffer
1) 为什么第一个表Using temporary
和Using filesort
?EXPLAIN
显示它正在使用索引zone_price
,该索引由 2 列组成:(zone, price_c)
。因此,在使用索引根据值选择行之后zone
,所有结果行都按 price_c 的顺序排列。并且由于查询是 ORDER BY price_c,因此根本不需要和Using temporary
。Using filesort
我错过了什么?
2) 对于第三张表,它应该使用索引work
。但是 ref 是NULL
。那是什么意思?work
由列组成。因此,当使用子句(ad,c,country)
从中选择行时,难道不应该只是简单的索引查找吗?中的值为4083,根据有 4113 行。这是否意味着 MySQL 正在执行完整索引扫描而不是查找?amp_c_countries
WHERE
(amp_c_countries.country = 'ES' AND amp_c.n = amp_c_countries.ad AND amp_c.camp = amp_c_countries.c)
rows
EXPLAIN
amp_c_countries
SHOW TABLE STATUS
3)关于如何解决上述两个问题,您有什么想法吗?amp_ads
包含TEXT
列,因此创建了大量磁盘临时表:
| Created_tmp_disk_tables | 906952 |
| Created_tmp_files | 11 |
| Created_tmp_tables | 912227 |
show processlist
还显示很多进程处于 状态Copying to tmp table
。
谢谢。感谢您的帮助。
编辑:
输出SHOW CREATE TABLE
:
mysql> SHOW CREATE TABLE `advertis_admpro`.`amp_c`\G
*************************** 1. row ***************************
Table: amp_c
Create Table: CREATE TABLE `amp_c` (
`n` int(10) unsigned NOT NULL DEFAULT '0',
`camp` tinyint(3) unsigned NOT NULL DEFAULT '0',
`zone` int(11) NOT NULL DEFAULT '0',
`javascript` tinyint(1) NOT NULL DEFAULT '0',
`banner_target` varchar(50) NOT NULL DEFAULT '',
`accept` tinyint(1) NOT NULL DEFAULT '0',
`en_u` tinyint(1) NOT NULL DEFAULT '0',
`en_w` tinyint(1) NOT NULL DEFAULT '0',
`i_got` int(10) unsigned NOT NULL DEFAULT '0',
`c_got` int(10) unsigned NOT NULL DEFAULT '0',
`r` double(4,2) unsigned NOT NULL DEFAULT '0.00',
`price_i` double(10,6) unsigned NOT NULL,
`price_c` double(10,3) unsigned NOT NULL,
`i_nu` int(11) NOT NULL DEFAULT '0',
`c_nu` int(11) NOT NULL DEFAULT '0',
`unlimit` tinyint(1) NOT NULL DEFAULT '0',
`d_total` int(10) unsigned NOT NULL DEFAULT '0',
`d_valid_by` int(10) unsigned NOT NULL DEFAULT '0',
`t1` int(10) unsigned NOT NULL DEFAULT '0',
`t2` int(10) unsigned NOT NULL DEFAULT '0',
`d1` tinyint(1) NOT NULL DEFAULT '0',
`d2` tinyint(1) NOT NULL DEFAULT '0',
`d3` tinyint(1) NOT NULL DEFAULT '0',
`d4` tinyint(1) NOT NULL DEFAULT '0',
`d5` tinyint(1) NOT NULL DEFAULT '0',
`d6` tinyint(1) NOT NULL DEFAULT '0',
`d7` tinyint(1) NOT NULL DEFAULT '0',
`tz1` tinyint(1) NOT NULL DEFAULT '0',
`tz2` tinyint(1) NOT NULL DEFAULT '0',
`tz3` tinyint(1) NOT NULL DEFAULT '0',
`tz4` tinyint(1) NOT NULL DEFAULT '0',
`tz5` tinyint(1) NOT NULL DEFAULT '0',
`some_countr` tinyint(1) NOT NULL DEFAULT '0',
`i_d_max` int(10) unsigned NOT NULL DEFAULT '0',
`c_d_max` int(10) unsigned NOT NULL DEFAULT '0',
`i_d_nu` int(10) unsigned NOT NULL DEFAULT '0',
`c_d_nu` int(10) unsigned NOT NULL DEFAULT '0',
`last` int(10) unsigned NOT NULL DEFAULT '0',
`user` int(10) unsigned NOT NULL DEFAULT '0',
`username` varchar(15) NOT NULL DEFAULT '',
`emailed` int(10) unsigned NOT NULL DEFAULT '0',
KEY `work` (`en_u`,`en_w`,`i_nu`,`c_nu`,`d_valid_by`,`unlimit`,`i_d_max`,`c_d_max`,`i_d_nu`,`c_d_nu`,`t1`,`t2`,`n`),
KEY `n_index` (`n`,`camp`),
KEY `zone_price` (`zone`,`price_c`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1
1 row in set (0.00 sec)
mysql> SHOW CREATE TABLE `advertis_admpro`.`amp_ads`\G
*************************** 1. row ***************************
Table: amp_ads
Create Table: CREATE TABLE `amp_ads` (
`n` int(10) unsigned NOT NULL AUTO_INCREMENT,
`title` varchar(255) NOT NULL DEFAULT '',
`ad_type` int(10) unsigned NOT NULL DEFAULT '0',
`accept` tinyint(1) NOT NULL DEFAULT '0',
`en_w` tinyint(1) NOT NULL DEFAULT '0',
`weight` tinyint(1) NOT NULL DEFAULT '0',
`w` smallint(5) unsigned NOT NULL DEFAULT '0',
`h` smallint(5) unsigned NOT NULL DEFAULT '0',
`norepeat` int(10) unsigned NOT NULL DEFAULT '0',
`campaigns` tinyint(1) unsigned NOT NULL DEFAULT '0',
`zones` text NOT NULL,
`keywords` text NOT NULL,
`banner` varchar(255) NOT NULL DEFAULT '',
`url` varchar(255) NOT NULL DEFAULT '',
`alt` varchar(255) NOT NULL DEFAULT '',
`raw` text NOT NULL,
`kind` varchar(40) NOT NULL DEFAULT '',
`javascript` tinyint(1) NOT NULL DEFAULT '0',
`ad_complete` tinyint(1) NOT NULL DEFAULT '0',
`url1` text NOT NULL,
`url2` text NOT NULL,
`url3` text NOT NULL,
`text1` text NOT NULL,
`text2` text NOT NULL,
`text3` text NOT NULL,
`text4` text NOT NULL,
`text5` text NOT NULL,
`text6` text NOT NULL,
`text7` text NOT NULL,
`text8` text NOT NULL,
`text9` text NOT NULL,
`text10` text NOT NULL,
`picture1` varchar(255) NOT NULL DEFAULT '',
`picture2` varchar(255) NOT NULL DEFAULT '',
`picture3` varchar(255) NOT NULL DEFAULT '',
`picture4` varchar(255) NOT NULL DEFAULT '',
`picture5` varchar(255) NOT NULL DEFAULT '',
`created` int(10) unsigned NOT NULL DEFAULT '0',
`user` int(11) NOT NULL DEFAULT '0',
`username` varchar(15) NOT NULL DEFAULT '',
`preview` text NOT NULL,
`def` tinyint(1) NOT NULL DEFAULT '0',
UNIQUE KEY `n` (`n`),
KEY `work` (`ad_type`,`accept`,`en_w`,`norepeat`,`ad_complete`,`def`)
) ENGINE=InnoDB AUTO_INCREMENT=1532 DEFAULT CHARSET=latin1
1 row in set (0.00 sec)
mysql> SHOW CREATE TABLE `advertis_admpro`.`amp_c_countries`\G
*************************** 1. row ***************************
Table: amp_c_countries
Create Table: CREATE TABLE `amp_c_countries` (
`ad` int(10) unsigned NOT NULL DEFAULT '0',
`c` tinyint(3) unsigned NOT NULL DEFAULT '0',
`country` varchar(5) NOT NULL DEFAULT '',
KEY `work` (`ad`,`c`,`country`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1
1 row in set (0.00 sec)
答案1
当值在条件中使用时,往往不使用索引OR
。(amp_c.zone = '24' OR amp_c.zone = '25')
可能更好地写为(
amp_c.zone BETWEEN '24' AND '25')`。
当索引出现在 OR 的一侧而不出现在另一侧时,通常不使用索引。使用amp_c.some_countr = '0' OR (...)
可能会使索引的使用无效。
优化器在处理简单的等式时效果更好。您可能需要外连接而不是内连接。