为啥查询速度有时快有时慢?
果儿妈 2014-01-16 04:18:22 D_TF_QUALITY表有1800W 的数据,
表结构
CREATE TABLE `D_TF_QUALITY` (
`cons_id` int(8) NOT NULL,
`tid` int(4) NOT NULL,
`strative_id` varchar(16) CHARACTER SET utf8 COLLATE utf8_bin NOT NULL,
`time_id` varchar(8) CHARACTER SET utf8 COLLATE utf8_bin NOT NULL,
`qua_id` varchar(4) CHARACTER SET utf8 COLLATE utf8_bin NOT NULL,
`sxdlbphd` decimal(16,6) DEFAULT NULL,
`sxdybphd` decimal(16,6) DEFAULT NULL,
`plpc` decimal(16,6) DEFAULT NULL,
`adypc` decimal(16,6) DEFAULT NULL,
`bdypc` decimal(16,6) DEFAULT NULL,
`cdypc` decimal(16,6) DEFAULT NULL,
`abxdypc` decimal(16,6) DEFAULT NULL,
`bcxdypc` decimal(16,6) DEFAULT NULL,
`caxdypc` decimal(16,6) DEFAULT NULL,
PRIMARY KEY (`cons_id`,`tid`,`strative_id`,`time_id`,`qua_id`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8;
查询语句:
select CONS_ID,MAX(SXDLBPHD) as MAX_SXDLBPHD from D_TF_QUALITY group by CONS_ID LIMIT 2000;
在没有开查询缓存的情况下,为啥查询速度有快有慢呢?最少也要30s,慢的时候几分钟,啥原因呀?