事务的4种隔离级别演示
作者：互联网
（每次修改事务的时候事务2需要关掉从新打开才能生效事务1开启的事务）
1.read uncommitted：读未提交
set global transaction isolation level read uncommitted;
事务一:
mysql> use db2 Database changed mysql> select * from account; +----+----------+---------+ | id | NAME | balance | +----+----------+---------+ | 1 | zhangsan | 500 | | 2 | lisi | 1500 | +----+----------+---------+ 2 rows in set (0.00 sec)
mysql> select * from account; +----+----------+---------+ | id | NAME | balance | +----+----------+---------+ | 1 | zhangsan | 1000 | | 2 | lisi | 1000 | +----+----------+---------+ 2 rows in set (0.00 sec) mysql> set global transaction isolation level read uncommitted; Query OK, 0 rows affected (0.00 sec) mysql> start transaction; Query OK, 0 rows affected (0.00 sec) mysql> UPDATE account SET balance = balance - 500 WHERE id = 1; Query OK, 1 row affected (0.00 sec) Rows matched: 1 Changed: 1 Warnings: 0 mysql> UPDATE account SET balance = balance + 500 WHERE id = 2; Query OK, 1 row affected (0.00 sec) Rows matched: 1 Changed: 1 Warnings: 0 mysql> rollback; Query OK, 0 rows affected (0.03 sec)
事务2：
mysql> use db2 Database changed mysql> select * from account; +----+----------+---------+ | id | NAME | balance | +----+----------+---------+ | 1 | zhangsan | 1000 | | 2 | lisi | 1000 | +----+----------+---------+ 2 rows in set (0.00 sec) mysql> start transaction; Query OK, 0 rows affected (0.00 sec) mysql> select * from account; +----+----------+---------+ | id | NAME | balance | +----+----------+---------+ | 1 | zhangsan | 500 | | 2 | lisi | 1500 | +----+----------+---------+ 2 rows in set (0.00 sec) mysql> select * from account; +----+----------+---------+ | id | NAME | balance | +----+----------+---------+ | 1 | zhangsan | 1000 | | 2 | lisi | 1000 | +----+----------+---------+ 2 rows in set (0.00 sec)
查看把钱给你了然后事务1回滚了事务二在进行查看就和以前前一样了
2.read committed：读已提交（Oracle）
事务1：
mysql> set global transaction isolation level read committed; Query OK, 0 rows affected (0.00 sec) mysql> update account set balance = 1000; Query OK, 0 rows affected (0.00 sec) Rows matched: 2 Changed: 0 Warnings: 0 mysql> start transaction; Query OK, 0 rows affected (0.00 sec) mysql> UPDATE account SET balance = balance - 500 WHERE id = 1; Query OK, 1 row affected (0.00 sec) Rows matched: 1 Changed: 1 Warnings: 0 mysql> UPDATE account SET balance = balance + 500 WHERE id = 2; Query OK, 1 row affected (0.00 sec) Rows matched: 1 Changed: 1 Warnings: 0 mysql> commit; Query OK, 0 rows affected (0.03 sec)
事务二：
mysql> use db2; Database changed mysql> select * from account; +----+----------+---------+ | id | NAME | balance | +----+----------+---------+ | 1 | zhangsan | 1000 | | 2 | lisi | 1000 | +----+----------+---------+ 2 rows in set (0.00 sec) mysql> start transaction; Query OK, 0 rows affected (0.00 sec) mysql> select * from account; +----+----------+---------+ | id | NAME | balance | +----+----------+---------+ | 1 | zhangsan | 1000 | | 2 | lisi | 1000 | +----+----------+---------+ 2 rows in set (0.00 sec) mysql> select * from account; +----+----------+---------+ | id | NAME | balance | +----+----------+---------+ | 1 | zhangsan | 500 | | 2 | lisi | 1500 | +----+----------+---------+ 2 rows in set (0.00 sec)
会出现不可重复读现象和幻读
3. repeatable read：可重复读（MySQL默认）
事务1：
mysql> set global transaction isolation level repeatable read; Query OK, 0 rows affected (0.00 sec) mysql> update account set balance = 1000; Query OK, 2 rows affected (0.07 sec) Rows matched: 2 Changed: 2 Warnings: 0 mysql> start transaction; Query OK, 0 rows affected (0.00 sec) mysql> UPDATE account SET balance = balance - 500 WHERE id = 1; Query OK, 1 row affected (0.00 sec) Rows matched: 1 Changed: 1 Warnings: 0 mysql> UPDATE account SET balance = balance + 500 WHERE id = 2; Query OK, 1 row affected (0.00 sec) Rows matched: 1 Changed: 1 Warnings: 0 mysql> commit; Query OK, 0 rows affected (0.04 sec)
事务2：
mysql> use db2 Database changed mysql> select * from account; +----+----------+---------+ | id | NAME | balance | +----+----------+---------+ | 1 | zhangsan | 500 | | 2 | lisi | 1500 | +----+----------+---------+ 2 rows in set (0.00 sec) mysql> select * from account; +----+----------+---------+ | id | NAME | balance | +----+----------+---------+ | 1 | zhangsan | 1000 | | 2 | lisi | 1000 | +----+----------+---------+ 2 rows in set (0.00 sec) mysql> start transaction; Query OK, 0 rows affected (0.00 sec) mysql> select * from account; +----+----------+---------+ | id | NAME | balance | +----+----------+---------+ | 1 | zhangsan | 1000 | | 2 | lisi | 1000 | +----+----------+---------+ 2 rows in set (0.00 sec) mysql> select * from account; +----+----------+---------+ | id | NAME | balance | +----+----------+---------+ | 1 | zhangsan | 1000 | | 2 | lisi | 1000 | +----+----------+---------+ 2 rows in set (0.00 sec) mysql> commit; Query OK, 0 rows affected (0.00 sec) mysql> select * from account; +----+----------+---------+ | id | NAME | balance | +----+----------+---------+ | 1 | zhangsan | 500 | | 2 | lisi | 1500 | +----+----------+---------+ 2 rows in set (0.00 sec)
事务1提交后事务二不提交的情况下进行查询读取的是上面一样的数据（可重复读取）
事务2提交后在进行查询才是事务1提交过来的数据
4. serializable ： 串行化
事务1：
mysql> set global transaction isolation level serializable; Query OK, 0 rows affected (0.00 sec) mysql> start transaction; Query OK, 0 rows affected (0.00 sec) mysql> UPDATE account SET balance = balance - 500 WHERE id = 1; Query OK, 1 row affected (0.00 sec) Rows matched: 1 Changed: 1 Warnings: 0 mysql> UPDATE account SET balance = balance + 500 WHERE id = 2; Query OK, 1 row affected (0.00 sec) Rows matched: 1 Changed: 1 Warnings: 0 mysql> commit; Query OK, 0 rows affected (0.06 sec)
事务2：
mysql> use db2; Database changed mysql> select * from account; +----+----------+---------+ | id | NAME | balance | +----+----------+---------+ | 1 | zhangsan | 500 | | 2 | lisi | 1500 | +----+----------+---------+ 2 rows in set (0.00 sec) mysql> start transaction; Query OK, 0 rows affected (0.00 sec) mysql> select * from account; +----+----------+---------+ | id | NAME | balance | +----+----------+---------+ | 1 | zhangsan | 0 | | 2 | lisi | 2000 | +----+----------+---------+ 2 rows in set (25.42 sec)
当事务1提交之后事务二才会显示出来
如果事务1不提交事务2进行查询不会查询出东西一直在哪里等待事务1的提交
（事务1提交后事务2马上会执行出来）
事务2光标一直在等待
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标签：rows,演示,隔离,0.00,sec,mysql,+----+----------+---------+,balance,级别 来源： https://www.cnblogs.com/pengtianyang/p/16517932.html