mysql事務操作

當把多個操作當做乙個事務時,這些操作具有一下特點:

mysql> select @@autocommit; # 檢視autocommit
+--------------+
| @@autocommit |
+--------------+
|            1 |
+--------------+
1 row in set (0.00 sec)
mysql> set @@autocommit=0;# 將autocommit設定為0,防止自動提交
query ok, 0 rows affected (0.00 sec)
mysql> select @@autocommit;
+--------------+
| @@autocommit |
+--------------+
|            0 |
+--------------+
1 row in set (0.00 sec)
mysql> start transaction;# 開始事務
query ok, 0 rows affected (0.00 sec)
mysql> update account set balance=balance-1000 where name='ada';
query ok, 1 row affected (0.00 sec)
rows matched: 1  changed: 1  warnings: 0
mysql> update account set balance=balance+1000 where name='bob';
query ok, 1 row affected (0.00 sec)
rows matched: 1  changed: 1  warnings: 0
mysql> select * from account;# 此時該資料表和其他地方的表不一樣了,因為修改還沒有持久化到磁碟資料庫
+----+------+---------+
| id | name | balance |
+----+------+---------+
|  1 | ada  |   -1000 |
|  2 | bob  |    6000 |
+----+------+---------+
2 rows in set (0.00 sec)
mysql> commit;# 提交事務,持久化到磁碟
query ok, 0 rows affected (0.00 sec)

mysql> select * from account;
+----+------+---------+
| id | name | balance |
+----+------+---------+
|  1 | ada  |    1000 |
|  2 | bob  |    4000 |
+----+------+---------+
2 rows in set (0.00 sec)
mysql> start transaction;
query ok, 0 rows affected (0.00 sec)
mysql> update account set balance=balance-1000 where name='bob';
query ok, 1 row affected (0.00 sec)
rows matched: 1  changed: 1  warnings: 0
mysql> update account set balance=balance+1000 where name='ada';
query ok, 1 row affected (0.00 sec)
rows matched: 1  changed: 1  warnings: 0
mysql> select * from account;
+----+------+---------+
| id | name | balance |
+----+------+---------+
|  1 | ada  |    2000 |
|  2 | bob  |    3000 |
+----+------+---------+
2 rows in set (0.00 sec)
mysql> rollback;# 事務回滾,撤銷開始事務之後的更改
query ok, 0 rows affected (0.00 sec)
mysql> select * from account;
+----+------+---------+
| id | name | balance |
+----+------+---------+
|  1 | ada  |    1000 |
|  2 | bob  |    4000 |
+----+------+---------+
2 rows in set (0.00 sec)

開啟兩個mysql客戶端命令列

命令列一

mysql> start transaction;
query ok, 0 rows affected (0.00 sec)
mysql> select * from account;
+----+------+---------+
| id | name | balance |
+----+------+---------+
|  1 | ada  |    2000 |
|  2 | bob  |    3000 |
+----+------+---------+
2 rows in set (0.00 sec)
mysql> update account set balance=balance-1000 where name='bob';
query ok, 1 row affected (0.00 sec)
rows matched: 1  changed: 1  warnings: 0
mysql> update account set balance=balance+1000 where name='ada';
query ok, 1 row affected (0.00 sec)
rows matched: 1  changed: 1  warnings: 0

一切正常執行,還未進行提交

命令列二

mysql> start transaction;
query ok, 0 rows affected (0.00 sec)
mysql> update account set balance=balance-1000 where name='bob';# 執行更改操作時會陷入等待,這是為了同步兩個程序,防止最後提交上的事務是其中乙個的提交結果,把另乙個提交結果覆蓋
error 1205 (hy000): lock wait timeout exceeded; try restarting transaction 
mysql>

當命令列一執行commit;後命令列二才能正常執行事務操作

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