MySQL中update修改數據與原數據相同是否會再次執行

小編給大家分享一下MySQL中update修改數據與原數據相同是否會再次執行，相信大部分人都還不怎么了解，因此分享這篇文章給大家參考一下，希望大家閱讀完這篇文章后大有收獲，下面讓我們一起去了解一下吧！

本文主要測試MySQL執行update語句時，針對與原數據（即未修改）相同的update語句會在MySQL內部重新執行嗎？

測試環境

• MySQL5.7.25
• Centos 7.4

binlog_format為ROW

參數

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)

測試步驟

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)

總結

在binlog_format=row和binlog_row_image=FULL時，由于MySQL 需要在 binlog 里面記錄所有的字段，所以在讀數據的時候就會把所有數據都讀出來，那么重復數據的update不會執行。即MySQL 調用了 InnoDB 引擎提供的“修改為 (1,55)”這個接口，但是引擎發現值與原來相同，不更新，直接返回

binlog_format為STATEMENT

參數

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)

測試步驟

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)

以上是MySQL中update修改數據與原數據相同是否會再次執行的所有內容，感謝各位的閱讀！相信大家都有了一定的了解，希望分享的內容對大家有所幫助，如果還想學習更多知識，歡迎關注億速云行業資訊頻道！