MySQL 5.6比MySQL 8更快

Question

我正在运行一个查询，它在MySQL5.6上比在MySQL8上更快。在MySQL5.6中大约需要4秒，而在MySQL8中需要32秒。根据MySQL文档，MySQL8更快，但我见过相反的情况。

查询：

select id 
from defaultitem 
where masterId='3b1e9726-12ea-4adf-a6ef-f0950075fec4' 
and mainID in ( 
    select id 
    from campaign 
    where deleteflag=0 
    and validflag=1 
    and deptid='9d9d7e0f-7256-4ac6-9398-378ae9a0239e')

显示create表：

defaultitem - CREATE TABLE `defaultitem` (
  `id` varchar(255) NOT NULL,
  `value` varchar(50) NOT NULL,
  `masterId` varchar(255) DEFAULT NULL,
  PRIMARY KEY (`id`),
  KEY `FK22505D768EC27364` (`masterId`),
  CONSTRAINT `FK22505D768EC27364` FOREIGN KEY (`masterId`) REFERENCES `combomaster` (`masterid`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 

campaign - CREATE TABLE `campaign` (
  `id` varchar(255) NOT NULL,
  `deptid` varchar(255) DEFAULT NULL,
  `deleteflag` tinyint(4) DEFAULT '0',
  `validflag` tinyint(4) DEFAULT '0',
  PRIMARY KEY (`id`),
  KEY `FK47DDEA51F157E732` (`deptid`),
  CONSTRAINT `FK47DDEA51F157E732` FOREIGN KEY (`deptid`) REFERENCES `dept` (`deptid`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 |


EXPLAIN query in MySQL5.6 - 
| id | select_type | table             | type   | possible_keys              | key                | key_len | ref                               | rows   | Extra                              |
+----+-------------+-------------------+--------+----------------------------+--------------------+---------+-----------------------------------+--------+------------------------------------+
|  1 | SIMPLE      | defaultitem | ref    | FK22505D768EC27364         | FK22505D768EC27364 | 768     | const                             | 812528 | Using index condition; Using where |
|  1 | SIMPLE      | campaign      | eq_ref | PRIMARY,FK47DDEA51F157E732 | PRIMARY            | 767     | db.defaultitem.mainID |      1 | Using where                        |
+----+-------------+-------------------+--------+----------------------------+--------------------+---------+-----------------------------------+--------+------------------------------------+


EXPLAIN QUERY in MySQL8 -
| id | select_type | table             | partitions | type | possible_keys              | key                | key_len | ref   | rows   | filtered | Extra       |
+----+-------------+-------------------+------------+------+----------------------------+--------------------+---------+-------+--------+----------+-------------+
|  1 | SIMPLE      | campaign      | NULL       | ref  | PRIMARY,FK47DDEA51F157E732 | FK47DDEA51F157E732 | 768     | const |     15 |     1.00 | Using where |
|  1 | SIMPLE      | defaultitem | NULL       | ref  | FK22505D768EC27364         | FK22505D768EC27364 | 768     | const | 787517 |    10.00 | Using where |
+----+-------------+-------------------+------------+------+----------------------------+--------------------+---------+-------+--------+----------+-------------+

两个版本中的innodb_buffer_pool_size是相同的。

我认为MySQL 8会更快。

Answer 1

您的查询在功能上与：

SELECT DISTINCT x.id  
  FROM defaultitem x
  JOIN campaign y
    ON y.id = x.mainid
   AND y.deleteflag = 0 
   AND y.validflag = 1 
   AND y.deptid = '9d9d7e0f-7256-4ac6-9398-378ae9a0239e'
 WHERE x.masterId = '3b1e9726-12ea-4adf-a6ef-f0950075fec4';

...so为什么不这样写呢？

(deptid，validflag，deleteflag)的某个组合上的键可能会有所帮助。