MySQL中update修改数据与原数据相同会再次执行吗

背景本文主要测试MySQL执行update语句时，针对与原数据（即未修改）相同的update语句会在MySQL内部重新执行吗？测试环境MySQL5.7.25Centos 7.4binlog_format为ROW参数root@localhost : (none) 04:53:15> show variables like ‘binlog_row_image’;+——————+——-+| Variable_name | Value |+——————+——-+| binlog_row_image | FULL |+——————+——-+1 row in set (0.00 sec)root@localhost : (none) 04:53:49> show variables like ‘binlog_format’; +—————+——-+| Variable_name | Value |+—————+——-+| binlog_format | ROW |+—————+——-+1 row in set (0.00 sec)root@localhost : test 05:15:14> show variables like ’transaction_isolation’;+———————–+—————–+| Variable_name | Value |+———————–+—————–+| transaction_isolation | REPEATABLE-READ |+———————–+—————–+1 row in set (0.00 sec)测试步骤session1root@localhost : test 04:49:48> begin;Query OK, 0 rows affected (0.00 sec)root@localhost : test 04:49:52> select * from test where id =1;+—-+——+——+——+| id | sid | mid | name |+—-+——+——+——+| 1 | 999 | 871 | NW |+—-+——+——+——+1 row in set (0.00 sec)root@localhost : (none) 04:54:03> show engine innodb status\Gshow master status\G…—LOG—Log sequence number 12090390Log flushed up to 12090390Pages flushed up to 12090390Last checkpoint at 120903810 pending log flushes, 0 pending chkp writes33 log i/o’s done, 0.00 log i/o’s/second*************************** 1. row *************************** File: mysql-bin.000001 Position: 154 Binlog_Do_DB: Binlog_Ignore_DB: Executed_Gtid_Set: 1 row in set (0.00 sec)session2root@localhost : test 04:47:45> update test set sid=55 where id =1;Query OK, 1 row affected (0.01 sec)Rows matched: 1 Changed: 1 Warnings: 0root@localhost : (none) 04:54:03> show engine innodb status\Gshow master status\G…—LOG—Log sequence number 12091486Log flushed up to 12091486Pages flushed up to 12091486Last checkpoint at 120914770 pending log flushes, 0 pending chkp writes39 log i/o’s done, 0.00 log i/o’s/second*************************** 1. row *************************** File: mysql-bin.000001 Position: 500 Binlog_Do_DB: Binlog_Ignore_DB: Executed_Gtid_Set: 8392d215-4928-11e9-a751-0242ac110002:11 row in set (0.00 sec)session1root@localhost : test 04:49:57> update test set sid=55 where id =1; Query OK, 0 rows affected (0.00 sec)Rows matched: 1 Changed: 0 Warnings: 0root@localhost : (none) 04:54:03> show engine innodb status\Gshow master status\G…—LOG—Log sequence number 12091486Log flushed up to 12091486Pages flushed up to 12091486Last checkpoint at 120914770 pending log flushes, 0 pending chkp writes39 log i/o’s done, 0.00 log i/o’s/second*************************** 1. row *************************** File: mysql-bin.000001 Position: 500 Binlog_Do_DB: Binlog_Ignore_DB: Executed_Gtid_Set: 8392d215-4928-11e9-a751-0242ac110002:11 row in set (0.00 sec)root@localhost : test 04:52:05> select * from test where id =1;+—-+——+——+——+| id | sid | mid | name |+—-+——+——+——+| 1 | 999 | 871 | NW |+—-+——+——+——+1 row in set (0.00 sec)root@localhost : test 04:52:42> commit;Query OK, 0 rows affected (0.00 sec)root@localhost : test 04:52:52> select * from test where id =1;+—-+——+——+——+| id | sid | mid | name |+—-+——+——+——+| 1 | 55 | 871 | NW |+—-+——+——+——+1 row in set (0.00 sec)总结在binlog_format=row和binlog_row_image=FULL时，由于MySQL 需要在 binlog 里面记录所有的字段，所以在读数据的时候就会把所有数据都读出来，那么重复数据的update不会执行。即MySQL 调用了 InnoDB 引擎提供的“修改为 (1,55)”这个接口，但是引擎发现值与原来相同，不更新，直接返回binlog_format为STATEMENT参数root@localhost : (none) 04:53:15> show variables like ‘binlog_row_image’;+——————+——-+| Variable_name | Value |+——————+——-+| binlog_row_image | FULL |+——————+——-+1 row in set (0.00 sec)root@localhost : (none) 05:16:08> show variables like ‘binlog_format’;+—————+———–+| Variable_name | Value |+—————+———–+| binlog_format | STATEMENT |+—————+———–+1 row in set (0.00 sec)root@localhost : test 05:15:14> show variables like ’transaction_isolation’;+———————–+—————–+| Variable_name | Value |+———————–+—————–+| transaction_isolation | REPEATABLE-READ |+———————–+—————–+1 row in set (0.00 sec)测试步骤session1root@localhost : test 05:16:42> begin;Query OK, 0 rows affected (0.00 sec)root@localhost : test 05:16:44> select * from test where id =1;+—-+——+——+——+| id | sid | mid | name |+—-+——+——+——+| 1 | 111 | 871 | NW |+—-+——+——+——+1 row in set (0.00 sec)root@localhost : (none) 05:16:51> show engine innodb status\Gshow master status\G…—LOG—Log sequence number 12092582Log flushed up to 12092582Pages flushed up to 12092582Last checkpoint at 120925730 pending log flushes, 0 pending chkp writes45 log i/o’s done, 0.00 log i/o’s/second*************************** 1. row *************************** File: mysql-bin.000001 Position: 154 Binlog_Do_DB: Binlog_Ignore_DB: Executed_Gtid_Set: 1 row in set (0.00 sec)session2root@localhost : test 05:18:30> update test set sid=999 where id =1;Query OK, 1 row affected (0.00 sec)Rows matched: 1 Changed: 1 Warnings: 0root@localhost : (none) 05:18:47> show engine innodb status\Gshow master status\G…—LOG—Log sequence number 12093678Log flushed up to 12093678Pages flushed up to 12093678Last checkpoint at 120936690 pending log flushes, 0 pending chkp writes51 log i/o’s done, 0.14 log i/o’s/second*************************** 1. row *************************** File: mysql-bin.000001 Position: 438 Binlog_Do_DB: Binlog_Ignore_DB: Executed_Gtid_Set: 8392d215-4928-11e9-a751-0242ac110002:11 row in set (0.00 sec)session1root@localhost : test 05:16:47> update test set sid=999 where id =1;Query OK, 0 rows affected (0.00 sec)Rows matched: 1 Changed: 0 Warnings: 0root@localhost : (none) 05:20:03> show engine innodb status\Gshow master status\G…—LOG—Log sequence number 12094504Log flushed up to 12094504Pages flushed up to 12094504Last checkpoint at 120944950 pending log flushes, 0 pending chkp writes56 log i/o’s done, 0.00 log i/o’s/second*************************** 1. row *************************** File: mysql-bin.000001 Position: 438 Binlog_Do_DB: Binlog_Ignore_DB: Executed_Gtid_Set: 8392d215-4928-11e9-a751-0242ac110002:11 row in set (0.00 sec)root@localhost : test 05:19:33> select * from test where id =1; +—-+——+——+——+| id | sid | mid | name |+—-+——+——+——+| 1 | 999 | 871 | NW |+—-+——+——+——+1 row in set (0.00 sec)root@localhost : test 05:20:44> commit;Query OK, 0 rows affected (0.01 sec)root@localhost : test 05:20:57> select * from test where id =1;+—-+——+——+——+| id | sid | mid | name |+—-+——+——+——+| 1 | 999 | 871 | NW |+—-+——+——+——+1 row in set (0.00 sec)总结在binlog_format=statement和binlog_row_image=FULL时，InnoDB内部认真执行了update语句，即“把这个值修改成 (1,999)“这个操作，该加锁的加锁，该更新的更新。一站式开发者服务，海量学习资源0元起！阿里热门开源项目、机器学习干货、开发者课程/工具、小微项目、移动研发等海量资源；更有开发者福利Kindle、技术图书幸运抽奖，100%中–》https://www.aliyun.com/acts/product-section-2019/developer?utm_content=g_1000047140本文作者：powdba阅读原文本文为云栖社区原创内容，未经允许不得转载。