SET [GLOBAL | SESSION] TRANSACTION
transaction_characteristic [, transaction_characteristic] ...
transaction_characteristic: {
    ISOLATION LEVEL level
  | access_mode
}
level: {
     REPEATABLE READ
   | READ COMMITTED
   | READ UNCOMMITTED
   | SERIALIZABLE
}
access_mode: {
     READ WRITE
   | READ ONLY
}

To set the transaction isolation level, use an ISOLATION LEVEL level clause. 要设置事务隔离级别，请使用ISOLATION LEVEL level子句。It is not permitted to specify multiple ISOLATION LEVEL clauses in the same SET TRANSACTION statement.不允许在同一SET TRANSACTION语句中指定多个ISOLATION LEVEL子句。

The default isolation level is REPEATABLE READ. 默认隔离级别为REPEATABLE READ。Other permitted values are READ COMMITTED, READ UNCOMMITTED, and SERIALIZABLE. 其他允许的值包括READ COMMITTED、READ UNCOMMITTED和SERIALIZABLE。For information about these isolation levels, see Section 15.7.2.1, “Transaction Isolation Levels”.有关这些隔离级别的信息，请参阅第15.7.2.1节，“事务隔离级别”。

To set the transaction access mode, use a READ WRITE or READ ONLY clause. 要设置事务访问模式，请使用READ WRITE或READ ONLY子句。It is not permitted to specify multiple access-mode clauses in the same SET TRANSACTION statement.不允许在同一SET TRANSACTION语句中指定多访问模式子句。

By default, a transaction takes place in read/write mode, with both reads and writes permitted to tables used in the transaction. 默认情况下，事务以读/写模式进行，同时允许对事务中使用的表进行读写。This mode may be specified explicitly using SET TRANSACTION with an access mode of READ WRITE.此模式可以使用具有读写访问模式的SET TRANSACTION显式指定。

If the transaction access mode is set to READ ONLY, changes to tables are prohibited. 如果事务访问模式设置为READ ONLY，则禁止更改表。This may enable storage engines to make performance improvements that are possible when writes are not permitted.这可能使存储引擎能够在不允许写入时实现性能改进。

In read-only mode, it remains possible to change tables created with the TEMPORARY keyword using DML statements. 在只读模式下，仍然可以使用DML语句更改使用TEMPORARY关键字创建的表。Changes made with DDL statements are not permitted, just as with permanent tables.与永久表一样，不允许使用DDL语句进行更改。

The READ WRITE and READ ONLY access modes also may be specified for an individual transaction using the START TRANSACTION statement.还可以使用START TRANSACTION语句为单个事务指定READ WRITE和READ ONLY访问模式。

You can set transaction characteristics globally, for the current session, or for the next transaction only:您可以为当前会话或仅为下一个事务全局设置事务特征：

A change to global transaction characteristics requires the CONNECTION_ADMIN privilege (or the deprecated SUPER privilege). 对全局事务特征的更改需要CONNECTION_ADMIN权限（或不推荐使用的SUPER权限）。Any session is free to change its session characteristics (even in the middle of a transaction), or the characteristics for its next transaction (prior to the start of that transaction).任何会话都可以自由地改变其会话特性（即使在事务的中间），也可以改变其下一个事务的特征（在该事务开始之前）。

To set the global isolation level at server startup, use the --transaction-isolation=level option on the command line or in an option file. 要在服务器启动时设置全局隔离级别，请在命令行或选项文件中使用---transaction-isolation=level选项。Values of level for this option use dashes rather than spaces, so the permissible values are READ-UNCOMMITTED, READ-COMMITTED, REPEATABLE-READ, or SERIALIZABLE.此选项的level值使用破折号而不是空格，因此允许的值为READ-UNCOMMITTED、READ-COMMITTED、REPEATABLE-READ或SERIALIZABLE。

Similarly, to set the global transaction access mode at server startup, use the --transaction-read-only option. 类似地，要在服务器启动时设置全局事务访问模式，请使用--transaction-read-only选项。The default is OFF (read/write mode) but the value can be set to ON for a mode of read only.默认值为OFF（读/写模式），但对于只读模式，该值可以设置为ON。

For example, to set the isolation level to REPEATABLE READ and the access mode to READ WRITE, use these lines in the [mysqld] section of an option file:例如，要将隔离级别设置为REPEATABLE READ，将访问模式设置为READ WRITE，请在选项文件的[mysqld]部分使用以下行：

[mysqld]
transaction-isolation = REPEATABLE-READ
transaction-read-only = OFF

At runtime, characteristics at the global, session, and next-transaction scope levels can be set indirectly using the SET TRANSACTION statement, as described previously. 在运行时，可以使用SET TRANSACTION语句间接设置全局、会话和下一个事务作用域级别的特征，如前所述。They can also be set directly using the SET statement to assign values to the transaction_isolation and transaction_read_only system variables:也可以使用SET语句直接设置它们，以便为系统变量transaction_isolation和transaction_read_only赋值：

The following tables show the characteristic scope level set by each SET TRANSACTION and variable-assignment syntax.下表显示了每个SET TRANSACTION和变量分配语法设置的特征范围级别。

It is possible to check the global and session values of transaction characteristics at runtime:可以在运行时检查事务特征的全局值和会话值：

SELECT @@GLOBAL.transaction_isolation, @@GLOBAL.transaction_read_only;
SELECT @@SESSION.transaction_isolation, @@SESSION.transaction_read_only;