MySQL执行update语句和原数据相同会再次执行吗

站长资源 2025/2/9 佚名

2 0 1

黑松山资源网 Design By www.paidiu.com

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

MySQL5.7.25
Centos 7.4

binlog_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

session1

root@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 12090390
Log flushed up to 12090390
Pages flushed up to 12090390
Last checkpoint at 12090381
0 pending log flushes, 0 pending chkp writes
33 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)

session2

root@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: 0

root@localhost : (none) 04:54:03> show engine innodb status\Gshow master status\G
...
---
LOG
---
Log sequence number 12091486
Log flushed up to 12091486
Pages flushed up to 12091486
Last checkpoint at 12091477
0 pending log flushes, 0 pending chkp writes
39 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-a751-0242ac110002:1
1 row in set (0.00 sec)

session1

root@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: 0

root@localhost : (none) 04:54:03> show engine innodb status\Gshow master status\G
...
---
LOG
---
Log sequence number 12091486
Log flushed up to 12091486
Pages flushed up to 12091486
Last checkpoint at 12091477
0 pending log flushes, 0 pending chkp writes
39 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-a751-0242ac110002:1
1 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

session1

root@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 12092582
Log flushed up to 12092582
Pages flushed up to 12092582
Last checkpoint at 12092573
0 pending log flushes, 0 pending chkp writes
45 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)

session2

root@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: 0

root@localhost : (none) 05:18:47> show engine innodb status\Gshow master status\G
...
---
LOG
---
Log sequence number 12093678
Log flushed up to 12093678
Pages flushed up to 12093678
Last checkpoint at 12093669
0 pending log flushes, 0 pending chkp writes
51 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-a751-0242ac110002:1
1 row in set (0.00 sec)

session1

root@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: 0

root@localhost : (none) 05:20:03> show engine innodb status\Gshow master status\G
...
---
LOG
---
Log sequence number 12094504
Log flushed up to 12094504
Pages flushed up to 12094504
Last checkpoint at 12094495
0 pending log flushes, 0 pending chkp writes
56 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-a751-0242ac110002:1
1 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。

好了，以上就是这篇文章的全部内容了，希望本文的内容对大家的学习或者工作具有一定的参考学习价值，谢谢大家对的支持。

mysql,update语句,mysql,update语句无效,mysql,update

黑松山资源网 Design By www.paidiu.com

广告合作：本站广告合作请联系QQ：858582 申请时备注：广告合作（否则不回）
免责声明：本站资源来自互联网收集,仅供用于学习和交流,请遵循相关法律法规,本站一切资源不代表本站立场,如有侵权、后门、不妥请联系本站删除！

黑松山资源网 Design By www.paidiu.com

评论“MySQL执行update语句和原数据相同会再次执行吗”

暂无评论...

MySQL执行update语句和原数据相同会再次执行吗

详解mysql基本操作详细(二)

Mysql经典高逼格/命令行操作(速成)(推荐)

评论“MySQL执行update语句和原数据相同会再次执行吗”

《魔兽世界》大逃杀！60人新游玩模式《强袭风暴》3月21日上线

更新日志

友情链接