同样的查询结果，为什么效率相差十倍？
数据库是mysql，attackrecord ，attackdtail_sort两个数据记录表，数据量都较大，router_if字典表，数据量较小。为什么方法一的效率会比方法二低许多倍？
方法一、
select t2.Id Id,t2.BaseLineId,t2.BaselineName,t2.Bid,t2.Type,t2.StartTime,t2.EndTime,t2.Bps,t2.Pps,t2.Status,t2.DetailTable,t3.RouterIp,t3.IfIndex
FROM attackdtail_sort t1 ,
(select * from attackrecord t where t.StartTime >= 1201017600281 and t.StartTime <= 1201104000281 ) t2,
(select RouterIp,IfIndex, Id AS rid from router_if) t3
where t1.AttackId = t2.Id and t1.ReportKey=’dstIp’ and t1.ReportKeyValue = ‘5.5.5.100’
and t2.Bid = t3.rid
order by StartTime DESC
方法二、
SELECT * from attackrecord t1,
（select AttackId from
attackdtail_sort t
where
t.ReportKey=’dstIp’ and t.ReportKeyValue = ‘5.5.5.100’ ) t2
where t1.StartTime >= 1201017600281 and t1.StartTime <= 1201104000281 and t1.Id=t2.AttackId
order by StartTime DESC
感觉上那些t1,t2,t3连表的时候是不用索引的，所以连接时都会把t1,t2,t3全部检索一次。
第二个只连了t1,t2，如果t1,t2连表时检索了n行，那么t1,t2,t3连表就连了 n*t3的行数 那么多行，就算你的t3很少也是有影响的，关键是索引用不到。
你把explain的结果贴出来看看。
我写个sql语句，你试试看，会不会更快：
SELECT * from attackrecord t1 join
（select AttackId from
attackdtail_sort t
where
t.ReportKey=’dstIp’ and t.ReportKeyValue = ‘5.5.5.100’ ) t2
on t1.Id=t2.AttackId where t1.StartTime > = 1201017600281 and t1.StartTime <= 1201104000281
order by StartTime DESC
