mysql子查询性能

我的SQL（带子查询）耗时很长（将近24小时）。使用子查询是否不利于性能

我的桌子如下

mysql> show create table eventnew;
CREATE TABLE `eventnew` (
  `id` int(50) NOT NULL AUTO_INCREMENT,
  `date` datetime DEFAULT NULL,
  `src_ip` int(10) unsigned DEFAULT NULL,
  `src_port` int(10) unsigned DEFAULT NULL,
  `dst_ip` int(10) unsigned DEFAULT NULL,
  `dst_port` int(10) unsigned DEFAULT NULL,
  `repo_ip` varchar(50) DEFAULT NULL,
  `link` varchar(50) DEFAULT NULL,
  `binary_hash` varchar(50) DEFAULT NULL,
  `sensor_id` varchar(50) DEFAULT NULL,
  `repox_ip` int(10) unsigned DEFAULT NULL,
  `flags` varchar(50) DEFAULT NULL,
  `shellcode` varchar(1000) DEFAULT NULL,
  PRIMARY KEY (`id`),
  KEY `date` (`date`),
  KEY `sensor_id` (`sensor_id`),
  KEY `src_ip` (`src_ip`)
) ENGINE=MyISAM AUTO_INCREMENT=883278 DEFAULT CHARSET=latin1

我的SQL如下所示：

SELECT COUNT( DISTINCT binary_hash ) AS cnt
FROM eventnew
WHERE DATE >=  '2010-10-16'
AND DATE <  '2010-10-17'
AND binary_hash NOT 
IN (

SELECT DISTINCT binary_hash
FROM eventnew
WHERE DATE <  '2010-10-16'
AND binary_hash IS NOT NULL
)

---

我建议您使用

不存在

而不是

不存在

使用子查询肯定会影响您的性能。例如，假设一个表T1有'n'记录，T2有'm'记录。当您在T1和T2上执行联接时，它将接受n*m条记录，然后将根据您的条件对它们进行排序。同样的情况也适用于关键字中的。如果子查询中有另一个约束，则会进一步降低效率。然而，在实践中无法避免使用子查询

试试这个

SELECT COUNT( DISTINCT a.binary_hash ) AS cnt
FROM eventnew a left join eventnew b on (a.binary_hash=b.binary_hash AND b.binary_hash IS NOT NULL AND b.DATE <  '2010-10-16')
WHERE a.DATE >=  '2010-10-16'
AND a.DATE <  '2010-10-17'
and  b.date is null

选择COUNT（不同的二进制散列）作为cnt
从eventnew a左连接eventnew b on（a.binary_hash=b.binary_hash，b.binary_hash不为空，b.DATE<'2010-10-16'）
其中a.DATE>=“2010-10-16”
日期<'2010-10-17'
日期为空

SELECT COUNT( DISTINCT a.binary_hash ) AS cnt
FROM eventnew a left join eventnew b on (a.binary_hash=b.binary_hash AND b.binary_hash IS NOT NULL AND b.DATE <  '2010-10-16')
WHERE a.DATE >=  '2010-10-16'
AND a.DATE <  '2010-10-17'
and  b.date is null