MySQL优化--NOT EXISTS和LEFT JOIN方式差异
在MySQL中，我们可以将NOT EXISTS语句转换为LEFT JOIN语句来进行优化，哪为什么会有性能提升呢？
使用NOT EXISTS方式SQL为：
SELECT count(1)
FROM t_monitor m
WHERE NOT exists
(SELECT 1
FROM t_alarm_realtime AS a
WHERE a.resource_id=m.resource_id
AND a.resource_type=m.resource_type
AND a.monitor_name=m.monitor_name)
而使用LEFT JOIN方式SQL为：
SELECT count(1)
FROM t_monitor m
LEFT JOIN t_alarm_realtime AS a
ON a.resource_id=m.resource_id
AND a.resource_type=m.resource_type
AND a.monitor_name=m.monitor_name
WHERE a.resource_id is NULL
从查询效果来看，NOT EXISTS 方式耗时29.38秒，而LEFT JOIN方式耗时1.20秒，性能提升25倍左右。
查看NOT EXISTS方式的执行计划：
*************************** 1. row ***************************
id: 1
select_type: PRIMARY
table: m
partitions: NULL
type: index
possible_keys: NULL
key: idx_id_name_type
key_len: 119
ref: NULL
rows: 578436
filtered: 100.00
Extra: Using where; Using index
*************************** 2. row ***************************
id: 2
select_type: DEPENDENT SUBQUERY
table: a
partitions: NULL
type: eq_ref
possible_keys: idx_id_name_type
key: idx_id_name_type
key_len: 119
ref: cmdb.m.resource_id,cmdb.m.monitor_name,cmdb.m.resource_type
rows: 1
filtered: 100.00
Extra: Using index
查看LEFT JOIN方式的执行计划：
*************************** 1. row ***************************
id: 1
select_type: SIMPLE
table: m
partitions: NULL
type: index
possible_keys: NULL
key: idx_id_name_type
key_len: 119
ref: NULL
rows: 578436
filtered: 100.00
Extra: Using index
*************************** 2. row ***************************
id: 1
select_type: SIMPLE
table: a
partitions: NULL
type: eq_ref
possible_keys: idx_id_name_type
key: idx_id_name_type
key_len: 119
ref: cmdb.m.resource_id,cmdb.m.monitor_name,cmdb.m.resource_type
rows: 1
filtered: 100.00
Extra: Using where; Not exists; Using index
使用SQL PROFILE查看NOT EXISTS 执行过程：
+--------------------+----------+----------+------------+-------------------+---------------------+--------------+---------------+
| Status | Duration | CPU_user | CPU_system | Context_voluntary | Context_involuntary | Block_ops_in | Block_ops_out |
+--------------------+----------+----------+------------+-------------------+---------------------+--------------+---------------+
| executing | 0.000023 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| Sending data | 0.000026 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| executing | 0.000023 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| Sending data | 0.000026 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| executing | 0.000022 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| Sending data | 0.000026 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| executing | 0.000023 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| Sending data | 0.000026 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| executing | 0.000023 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| Sending data | 0.000026 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| executing | 0.000023 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| Sending data | 0.000028 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| executing | 0.000022 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| Sending data | 0.000026 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| executing | 0.000023 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| Sending data | 0.000026 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| executing | 0.000023 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| Sending data | 0.000026 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| executing | 0.000023 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| Sending data | 0.000026 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| executing | 0.000023 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| Sending data | 0.000026 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| executing | 0.000023 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| Sending data | 0.000029 | 0.001000 | 0.000000 | 0 | 0 | 0 | 0 |
| executing | 0.000023 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| Sending data | 0.000026 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| executing | 0.000022 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| Sending data | 0.000026 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| executing | 0.000023 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| Sending data | 0.000027 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| executing | 0.000023 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| Sending data | 0.000026 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| executing | 0.000023 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| Sending data | 0.000026 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| executing | 0.000023 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| Sending data | 0.000026 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| executing | 0.000023 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| Sending data | 0.000026 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| executing | 0.000023 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| Sending data | 0.000026 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| executing | 0.000023 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| Sending data | 0.000026 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| executing | 0.000023 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| Sending data | 0.000026 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| executing | 0.000023 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| Sending data | 0.000026 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| executing | 0.000023 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| Sending data | 0.000028 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| executing | 0.000023 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| Sending data | 0.000026 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| executing | 0.000023 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| Sending data | 0.000026 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| executing | 0.000023 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| Sending data | 0.000026 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| executing | 0.000023 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| Sending data | 0.000026 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| executing | 0.000023 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| Sending data | 0.000026 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| executing | 0.000023 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| Sending data | 0.000026 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| executing | 0.000023 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| Sending data | 0.000026 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| executing | 0.000023 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| Sending data | 0.000026 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| executing | 0.000025 | 0.000000 | 0.000999 | 0 | 0 | 0 | 0 |
| Sending data | 0.000031 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| executing | 0.000023 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| Sending data | 0.000028 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| executing | 0.000023 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| Sending data | 0.000027 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| executing | 0.000023 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| Sending data | 0.000027 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| executing | 0.000023 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| Sending data | 0.000027 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| executing | 0.000023 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| Sending data | 0.000027 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| executing | 0.000023 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| Sending data | 0.000027 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| executing | 0.000023 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| Sending data | 0.000027 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| executing | 0.000023 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| Sending data | 0.000027 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| executing | 0.000023 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| Sending data | 0.000028 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| executing | 0.000023 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| Sending data | 0.000027 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| executing | 0.000023 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| Sending data | 0.000027 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| executing | 0.000022 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| Sending data | 0.000027 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| executing | 0.000023 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| Sending data | 0.000027 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| executing | 0.000023 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| Sending data | 0.000033 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| end | 0.000024 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| query end | 0.000028 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| closing tables | 0.000027 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| freeing items | 0.000039 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| logging slow query | 0.000059 | 0.000000 | 0.000000 | 0 | 0 | 0 | 16 |
| cleaning up | 0.000033 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
+--------------------+----------+----------+------------+-------------------+---------------------+--------------+---------------+
使用SQL PROFILE查看LEFT JOIN 执行过程：
+----------------------+----------+----------+------------+-------------------+---------------------+--------------+---------------+
| Status | Duration | CPU_user | CPU_system | Context_voluntary | Context_involuntary | Block_ops_in | Block_ops_out |
+----------------------+----------+----------+------------+-------------------+---------------------+--------------+---------------+
| starting | 0.000162 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| checking permissions | 0.000025 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| checking permissions | 0.000025 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| Opening tables | 0.000033 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| init | 0.000049 | 0.001000 | 0.000000 | 0 | 0 | 0 | 0 |
| System lock | 0.000030 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| optimizing | 0.000033 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| statistics | 0.000050 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| preparing | 0.000037 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| executing | 0.000025 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| Sending data | 1.200899 | 1.547764 | 0.124981 | 7460 | 116 | 0 | 8608 |
| end | 0.000103 | 0.000000 | 0.000000 | 2 | 0 | 0 | 0 |
| query end | 0.000028 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| closing tables | 0.000028 | 0.000000 | 0.000000 | 0 | 0 | 0 | 0 |
| freeing items | 0.000039 | 0.000000 | 0.000000 | 2 | 0 | 0 | 8 |
| logging slow query | 0.000052 | 0.000000 | 0.000000 | 0 | 0 | 0 | 24 |
| cleaning up | 0.000030 | 0.000000 | 0.000000 | 1 | 0 | 0 | 0 |
+----------------------+----------+----------+------------+-------------------+---------------------+--------------+---------------+
两种执行方式对比：
1、从执行计划来看，两个表都使用了索引，区别在于NOT EXISTS使用“DEPENDENT SUBQUERY”方式，而LEFT JOIN使用普通表关联的方式
2、从执行过程来看，LEFT JOIN方式主要消耗Sending data的上，在NOT EXISTS方式主要消耗在"executing"和“Sending data”两项上，受限于PROFILE只能记录100行结果，因此超过57万个"executing"和“Sending data”的组合项没有显示，虽然每次"executing"和“Sending data”的组合项消耗时间较少（约50毫秒），但由于执行次数较高，导致最终执行时间较长（50μs*578436=28921800us=28.92s）
如何在NOT EXISTS和LEFT JOIN中选择：
1、当外层数据较少时，子查询循环次数较少，使用NOT EXISTS并不会导致严重的性能问题，推荐使用NOT EXISTS方式。
2、当外层数据较大时，子查询消耗随外层数据量递增，查询性能较差，推荐使用LEFT JOIN方式
总结：
按照存在即合理是客观唯心主义的理论，NOT EXISTS以更直观地方式实现业务需求，在SQL复杂度上要远低于LEFT JOIN，且在生产执行计划时，NOT EXISTS方式相对更稳定些，LEFT JOIN可能会随统计信息变化而生产不同的执行计划。
MySQL优化--NOT EXISTS和LEFT JOIN方式差异的更多相关文章
- 0104探究MySQL优化器对索引和JOIN顺序的选择
转自http://www.jb51.net/article/67007.htm,感谢博主 本文通过一个案例来看看MySQL优化器如何选择索引和JOIN顺序.表结构和数据准备参考本文最后部分" ...
- 性能优化之mysql优化——慢查日志的开启方式和存储
-- MySQL优化 -- mysql 慢查日志的开启方式和存储 -- 1) 查看mysql是否开启慢查询日志 SHOW VARIABLES LIKE 'slow_query_log'; -- 2) ...
- sql优化 表连接join方式
sql优化核心 是数据库中 解析器+优化器的工作,我觉得主要有以下几个大方面:1>扫表的方法(索引非索引.主键非主键.书签查.索引下推)2>关联表的方法(三种),关键是内存如何利用 ...
- 如何干涉MySQL优化器使用hash join
GreatSQL社区原创内容未经授权不得随意使用,转载请联系小编并注明来源. GreatSQL是MySQL的国产分支版本,使用上与MySQL一致. 前言 实验 总结 前言 数据库的优化器相当于人类的大 ...
- SQL优化--使用 EXISTS 代替 IN 和 inner join来选择正确的执行计划
在使用Exists时,如果能正确使用,有时会提高查询速度: 1,使用Exists代替inner join 2,使用Exists代替 in 1,使用Exists代替inner join例子: 在一般写s ...
- MySQL优化—工欲善其事，必先利其器之EXPLAIN(转)
最近慢慢接触MySQL,了解如何优化它也迫在眉睫了,话说工欲善其事,必先利其器.最近我就打算了解下几个优化MySQL中经常用到的工具.今天就简单介绍下EXPLAIN. 内容导航 id select_t ...
- MySQL优化—工欲善其事，必先利其器之EXPLAIN
最近慢慢接触MySQL,了解如何优化它也迫在眉睫了,话说工欲善其事,必先利其器.最近我就打算了解下几个优化MySQL中经常用到的工具.今天就简单介绍下EXPLAIN. 内容导航 id select_t ...
- mysql优化sql语句的方法
1.对查询进行优化,应尽量避免全表扫描,首先应考虑在 where 及 order by 涉及的列上建立索引. 2.应尽量避免在 where 子句中使用!=或<>操作符,否则将引擎放弃使用索 ...
- 项目中常用的19条MySQL优化
声明一下:下面的优化方案都是基于 " Mysql-索引-BTree类型 " 的 一.EXPLAIN 做MySQL优化,我们要善用 EXPLAIN 查看SQL执行计划. 下面来个简单 ...
随机推荐
- Python实践练习：强口令检测
题目: 写一个函数,它使用正则表达式,确保传入的口令字符串是强口令.强口令的定义是:长度不少于 8 个字符,同时包含大写和小写字符,至少有一位数字.你可能需要用多个正则表达式来测试该字符串,以保证它的 ...
- __enter__ 和 __exit__上下文管理协议
class F: def __init__(self,n): self.n = n def __enter__(self): print('执行enter') return self def __ex ...
- ORM的相关操作
http://www.cnblogs.com/liwenzhou/p/8660826.html
- SQL With (递归CTE查询)
指定临时命名的结果集,这些结果集称为公用表表达式 (CTE).该表达式源自简单查询,并且在单条 SELECT.INSERT.UPDATE 或 DELETE 语句的执行范围内定义.该子句也可用在 CRE ...
- 尚硅谷springboot学习30-docker安装mysql示例
docker pull mysql 错误的启动示例 错误日志:需要设置密码 正确的启动 但还不能直接使用,因为没有做端口映射,外界无法连接 可用的启动 连接成功 几个高级的操作 指定配置文件 dock ...
- 利用nginx添加账号密码验证
server { listen ; server_name xxx.com; location / { proxy_pass http://10.10.10.10:5601; proxy_redire ...
- Linux命令:unlias
语法 unalias [-a] name [name ...] 说明 取消别名. 可以一次取消多个别名,写几个取消几个.不写,取消所有别名. 参数 -a 取消所有别名,不论后面是否跟一个还是多个nam ...
- H5页面input输入框含有键盘自带的表情符时显示异常
在做一个关于新闻的评论功能的H5页面时,需求里面要求能够发送表情显示表情,如果使用自定义的表情库,则在评论也还要加载大量的表情符图片,极大的影响加载速度,消耗流量,去看了下别的新闻网页版的评论部分也没 ...
- 微信小程序页面跳转 的几种方式
最近在做微信小程序,碰到页面跳转的问题,总结一下页面之间跳转的方式 一.wx.navigateTo(OBJECT) 这是最普遍的一种跳转方式,其官方解释为:“保留当前页面,跳转到应用内的某个页面” 类 ...
- Java学习笔记（十九）：Object类