这里是日志输出:帮助消除MySQL的文件排序
# Time: 100915 13:06:49
# [email protected]: ss[ss] @ localhost []
# Query_time: 13.978355 Lock_time: 0.000029 Rows_sent: 10 Rows_examined: 562760
use ss;
SET timestamp=1284574009;
SELECT DISTINCT
SQL_CALC_FOUND_ROWS
B.*,
U.username
FROM sc_users AS U,
sc_bookmarks AS B
WHERE B.uId = U.uId
AND B.bStatus = 0
GROUP BY B.bHash
ORDER BY B.bModified DESC
LIMIT 10;
和解释输出:
id select_type table type possible_keys key key_len ref rows Extra
----------------------------------------------------------------------------------------------------
1 SIMPLE U ALL PRIMARY NULL NULL NULL 2 Using temporary; Using filesort
1 SIMPLE B ALL sc_bookmarks_usd NULL NULL NULL 187586 Using where; Using join buffer
更新:这是由于sc_users创建语句OMGPonies/BrianHooper :-)
CREATE TABLE `sc_users` (
`uId` int(11) NOT NULL AUTO_INCREMENT,
`username` varchar(25) NOT NULL DEFAULT '',
`password` varchar(40) NOT NULL DEFAULT '',
`uDatetime` datetime NOT NULL DEFAULT '0000-00-00 00:00:00',
`uModified` datetime NOT NULL DEFAULT '0000-00-00 00:00:00',
`name` varchar(50) DEFAULT NULL,
`email` varchar(50) NOT NULL DEFAULT '',
`homepage` varchar(255) DEFAULT NULL,
`uContent` text,
PRIMARY KEY (`uId`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8 AUTO_INCREMENT=3 ;
更多详细资料(感谢马克·拜尔斯):
该查询由开源项目semanticscuttle生成以生成主页。我不知道为什么查询是按原样写的,因为我只是在这个项目中弄湿了我的脚。 You can see the source where this sql is generated here though.
我已经尝试添加各种索引和组合索引,没有运气加快查询或删除文件扫描。任何提示都表示赞赏!
更新:减慢是由ORDER BY语句造成的...... 查询波纹管在4秒内以ORDER BY运行,0.01秒内没有它。 任何想法为什么/如何解决它?
SELECT DISTINCT SQL_CALC_FOUND_ROWS B.*, U.username
FROM sc_users AS U, sc_bookmarks AS B
WHERE B.uId = U.uId
AND B.bStatus = 0
GROUP BY B.bHash
ORDER BY B.bModified DESC
更新:全新SQL和索引Quassnoi在回答中波纹管......这对我来说看起来很大,但实际上增加了执行时间,并没有摆脱文件各种各样的:
EXPLAIN SELECT SQL_CACHE b.*, u.username FROM ( SELECT DISTINCT bHash FROM sc_bookmarks b WHERE bStatus = 0 ) bd JOIN sc_bookmarks b ON b.bId = ( SELECT bId FROM sc_bookmarks bi WHERE bi.bStatus = 0 AND bi.bHash = bd.bHash ORDER BY bStatus DESC, bHash DESC, bModified DESC, bId DESC LIMIT 1 ) JOIN sc_users u ON u.uId = b.uId ORDER BY bModified ASC LIMIT 10;
+----+--------------------+------------+--------+--------------------------+------------------+---------+----------+--------+---------------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+--------------------+------------+--------+--------------------------+------------------+---------+----------+--------+---------------------------------+
| 1 | PRIMARY | <derived2> | ALL | NULL | NULL | NULL | NULL | 187565 | Using temporary; Using filesort |
| 1 | PRIMARY | b | eq_ref | PRIMARY,sc_bookmarks_usd | PRIMARY | 4 | func | 1 | Using where |
| 1 | PRIMARY | u | eq_ref | PRIMARY,su_idx | PRIMARY | 4 | ss.b.uId | 1 | |
| 3 | DEPENDENT SUBQUERY | bi | ref | sc_bookmarks_hui,bStatus | sc_bookmarks_hui | 98 | bd.bHash | 1 | Using where; Using filesort |
| 2 | DERIVED | b | ref | bStatus | bStatus | 1 | | 94556 | Using where; Using index |
+----+--------------------+------------+--------+--------------------------+------------------+---------+----------+--------+---------------------------------+
更新:根据Quassnoi的请求,这里是sc_bookmarks的CREATE TABLE语句。
CREATE TABLE `sc_bookmarks` (
`bId` int(11) NOT NULL AUTO_INCREMENT,
`uId` int(11) NOT NULL DEFAULT '0',
`bIp` varchar(40) DEFAULT NULL,
`bStatus` tinyint(1) NOT NULL DEFAULT '0',
`bDatetime` datetime NOT NULL DEFAULT '0000-00-00 00:00:00',
`bModified` datetime NOT NULL DEFAULT '0000-00-00 00:00:00',
`bTitle` varchar(255) NOT NULL DEFAULT '',
`bAddress` varchar(1500) NOT NULL,
`bDescription` text,
`bPrivateNote` text,
`bHash` varchar(32) NOT NULL DEFAULT '',
`bVotes` int(11) NOT NULL,
`bVoting` int(11) NOT NULL,
`bShort` varchar(16) DEFAULT NULL,
PRIMARY KEY (`bId`),
KEY `sc_bookmarks_usd` (`uId`,`bStatus`,`bDatetime`),
KEY `sc_bookmarks_hui` (`bHash`,`uId`,`bId`),
KEY `sc_bookmarks_du` (`bDatetime`,`uId`),
KEY `sc_bookmarks_modified_idx` (`bModified`),
KEY `bStatus` (`bStatus`,`bHash`,`bModified`,`uId`,`bId`),
KEY `bHash` (`bHash`),
CONSTRAINT `sc_bookmarks_ibfk_1` FOREIGN KEY (`uId`) REFERENCES `sc_users` (`uId`),
CONSTRAINT `sc_bookmarks_ibfk_2` FOREIGN KEY (`uId`) REFERENCES `sc_users` (`uId`)
) ENGINE=InnoDB AUTO_INCREMENT=187566 DEFAULT CHARSET=utf8
更新jacobs反馈cwiske的答案。 该查询已经过优化,但不会返回与原始查询相同的结果。
例如,我在表“sc_bookmarks”中有3个条目。
bId bModified bHash
------------------------------------
2000-11-10 aaaaaa ...
2011-12-12 bbbbbb ...
2010-11-11 aaaaaa ...
该查询应该只返回行ID为1和2.但它会返回所有3条记录。好像MySQL不喜欢:'GROUP BY B.bModified DESC,B.bHash DESC'
我试图改变'GROUP BY B.bModified DESC,B.bHash DESC'
到'GROUP基于B .bModified,B.bHash GROUP BY B.bHash,B.bModified'
但我仍然得到所有3条记录。
它在我离开'通过B.bHash组群'时工作,但阻止索引工作。
filesort在'sc_users'表上 - 请为它发布CREATE TABLE语句。 – 2010-09-15 22:16:16
当您拥有GROUP BY时,DISTINCT的用途是什么? GROUP BY是否已经保证结果集中B.bHash的值是不同的?你是否意识到,在结果中包含不在组中的列可能会导致在某些情况下不确定的结果?也许你可以解释你想做什么? – 2010-09-15 22:23:05
呃...它看起来像你张贴错误的表的代码... – 2010-09-16 13:36:07