设置MySQL事务隔离级别 transaction

MySQL支持四种隔离级别，分别是：

0 --> 读未提交 （READ-UNCOMMITTED）

1 --> 读已提交 （READ-COMMITTED）

2 --> 可重复读 （REPEATABLE-READ）

3 --> 序列化  （SERIALIZABLE）

设置隔离级别的方法是：

SET [SESSION|GLOBAL] transaction_isolation=[0|1|2|3];

查看隔离级别的方法是：

SHOW [GLOBAL] VARIABLES LIKE 'transaction_isolation';

mysql>  set global transaction_isolation=0;
Query OK, 0 rows affected (0.00 sec)

mysql> show global variables like 'transaction_isolation';
+-----------------------+------------------+
| Variable_name         | Value            |
+-----------------------+------------------+
| transaction_isolation | READ-UNCOMMITTED |
+-----------------------+------------------+
1 row in set (0.01 sec)

mysql>  set global transaction_isolation=1;
Query OK, 0 rows affected (0.00 sec)

mysql> show global variables like 'transaction_isolation';
+-----------------------+----------------+
| Variable_name         | Value          |
+-----------------------+----------------+
| transaction_isolation | READ-COMMITTED |
+-----------------------+----------------+
1 row in set (0.00 sec)

set global transaction_isolation=2;

mysql> show global variables like 'transaction_isolation';
+-----------------------+-----------------+
| Variable_name         | Value           |
+-----------------------+-----------------+
| transaction_isolation | REPEATABLE-READ |
+-----------------------+-----------------+
1 row in set (0.00 sec)

mysql>  set global transaction_isolation=3;
Query OK, 0 rows affected (0.00 sec)

mysql> show global variables like 'transaction_isolation';
+-----------------------+--------------+
| Variable_name         | Value        |
+-----------------------+--------------+
| transaction_isolation | SERIALIZABLE |
+-----------------------+--------------+
1 row in set (0.00 sec)