START TRANSACTION
    [transaction_characteristic [, transaction_characteristic] ...]

transaction_characteristic: {
    WITH CONSISTENT SNAPSHOT
  | READ WRITE
  | READ ONLY
}

BEGIN [WORK]
COMMIT [WORK] [AND [NO] CHAIN] [[NO] RELEASE]
ROLLBACK [WORK] [AND [NO] CHAIN] [[NO] RELEASE]
SET autocommit = {0 | 1}

这些语句提供了对事务使用的控制：These statements provide control over use of transactions:

默认情况下，MySQL 在启用 自动提交 模式下运行。这意味着，当不处于事务中时，每个语句都是原子性的，就像它们被 START TRANSACTION 和 COMMIT 包围一样。您不能使用 ROLLBACK 来撤销效果；但是，如果在语句执行过程中发生错误，该语句将回滚。By default, MySQL runs with autocommit mode enabled. This means that, when not otherwise inside a transaction, each statement is atomic, as if it were surrounded by START TRANSACTION and COMMIT. You cannot use ROLLBACK to undo the effect; however, if an error occurs during statement execution, the statement is rolled back.

要在单次语句序列中隐式禁用自动提交模式，请使用 START TRANSACTION 语句：To disable autocommit mode implicitly for a single series of statements, use the START TRANSACTION statement:

START TRANSACTION;
SELECT @A:=SUM(salary) FROM table1 WHERE type=1;
UPDATE table2 SET summary=@A WHERE type=1;
COMMIT;

使用 START TRANSACTION 时，自动提交保持禁用，直到您通过 COMMIT 或 ROLLBACK 结束事务。然后自动提交模式恢复到先前状态。With START TRANSACTION, autocommit remains disabled until you end the transaction with COMMIT or ROLLBACK. The autocommit mode then reverts to its previous state.

START TRANSACTION 允许使用多个修饰符来控制事务特性。要指定多个修饰符，请用逗号分隔它们。START TRANSACTION permits several modifiers that control transaction characteristics. To specify multiple modifiers, separate them by commas.

要显式禁用自动提交模式，请使用以下语句：To disable autocommit mode explicitly, use the following statement:

SET autocommit=0;

通过将 autocommit 变量设置为零来禁用自动提交模式后，对事务安全表（例如 InnoDB 或 NDB 表）的更改不会立即生效。您必须使用 COMMIT 将更改保存到磁盘，或使用 ROLLBACK 忽略更改。After disabling autocommit mode by setting the autocommit variable to zero, changes to transaction-safe tables (such as those for InnoDB or NDB) are not made permanent immediately. You must use COMMIT to store your changes to disk or ROLLBACK to ignore the changes.

autocommit 是会话变量，必须针对每个会话进行设置。要为每个新连接禁用自动提交模式，请参阅 autocommit 系统变量在 第 7.1.8 节，“服务器系统变量” 的描述。autocommit is a session variable and must be set for each session. To disable autocommit mode for each new connection, see the description of the autocommit system variable at Section 7.1.8, “Server System Variables”.

BEGIN 和 BEGIN WORK 被支持作为 START TRANSACTION 的别名，用于启动事务。START TRANSACTION 是标准 SQL 语法，是启动临时事务的推荐方式，并且允许 BEGIN 所不支持的修饰符。BEGIN and BEGIN WORK are supported as aliases of START TRANSACTION for initiating a transaction. START TRANSACTION is standard SQL syntax, is the recommended way to start an ad-hoc transaction, and permits modifiers that BEGIN does not.

BEGIN 语句与用于开始 BEGIN ... END 复合语句的 BEGIN 关键字不同。后者并不开始一个事务。参见 第 15.6.1 节，“BEGIN ... END 复合语句”。The BEGIN statement differs from the use of the BEGIN keyword that starts a BEGIN ... END compound statement. The latter does not begin a transaction. See Section 15.6.1, “BEGIN ... END Compound Statement”.

可选的 WORK 关键字支持用于 COMMIT 和 ROLLBACKCHAIN 和 RELEASE 子句也支持。CHAIN 和 RELEASE可用于对事务完成的额外控制。completion_type 系统变量的值决定了默认的完成行为。参见 第 7.1.8 节，“服务器系统变量”。The optional WORK keyword is supported for COMMIT and ROLLBACK, as are the CHAIN and RELEASE clauses. CHAIN and RELEASE can be used for additional control over transaction completion. The value of the completion_type system variable determines the default completion behavior. See Section 7.1.8, “Server System Variables”.

AND CHAIN 子句会在当前事务结束后立即启动新事务，且新事务的隔离级别与刚刚终止的事务相同。新事务还使用与刚刚终止事务相同的访问模式（READ WRITE 或 READ ONLY）。RELEASE 子句会导致服务器在终止当前事务后断开当前客户端会话。包含 NO 关键字会抑制 CHAIN 或 RELEASE 完成，如果系统变量默认设置为导致链式或释放完成，completion_typeThe AND CHAIN clause causes a new transaction to begin as soon as the current one ends, and the new transaction has the same isolation level as the just-terminated transaction. The new transaction also uses the same access mode (READ WRITE or READ ONLY) as the just-terminated transaction. The RELEASE clause causes the server to disconnect the current client session after terminating the current transaction. Including the NO keyword suppresses CHAIN or RELEASE completion, which can be useful if the completion_type system variable is set to cause chaining or release completion by default.

开始事务会提交任何待处理事务。更多信息请参见 第 15.3.3 节，“导致隐式提交的语句”。Beginning a transaction causes any pending transaction to be committed. See Section 15.3.3, “Statements That Cause an Implicit Commit”, for more information.

开始事务还会导致以 LOCK TABLES的表锁释放，就像你执行了 UNLOCK TABLES。开始事务不会释放通过 FLUSH TABLES WITH READ LOCK“。Beginning a transaction also causes table locks acquired with LOCK TABLES to be released, as though you had executed UNLOCK TABLES. Beginning a transaction does not release a global read lock acquired with FLUSH TABLES WITH READ LOCK.

为了获得最佳效果，事务应仅使用由单个事务安全存储引擎管理的表执行。否则，可能出现以下问题：For best results, transactions should be performed using only tables managed by a single transaction-safe storage engine. Otherwise, the following problems can occur:

每个事务在COMMIT时作为一个整体存储在二进制日志中。回滚的事务不会被记录。(例外：对非事务表的修改无法回滚。如果回滚的事务包含对非事务表的修改，则整个事务会记录在二进制日志中，并在末尾添加一个ROLLBACK语句，以确保对非事务表的修改被复制。) 参见第 7.4.4 节，“二进制日志”。Each transaction is stored in the binary log in one chunk, upon COMMIT. Transactions that are rolled back are not logged. (Exception: Modifications to nontransactional tables cannot be rolled back. If a transaction that is rolled back includes modifications to nontransactional tables, the entire transaction is logged with a ROLLBACK statement at the end to ensure that modifications to the nontransactional tables are replicated.) See Section 7.4.4, “The Binary Log”.

可以使用SET TRANSACTION语句更改事务的隔离级别或访问模式。参见第 15.3.7 节，“SET TRANSACTION 语句”。You can change the isolation level or access mode for transactions with the SET TRANSACTION statement. See Section 15.3.7, “SET TRANSACTION Statement”.

回滚可能是一个较慢的操作，并且可能隐式发生，而用户并未显式请求（例如，当发生错误时）。因此，SHOW PROCESSLIST在会话的State列中显示Rolling back，不仅适用于使用ROLLBACK语句执行的显式回滚，也适用于隐式回滚。Rolling back can be a slow operation that may occur implicitly without the user having explicitly asked for it (for example, when an error occurs). Because of this, SHOW PROCESSLIST displays Rolling back in the State column for the session, not only for explicit rollbacks performed with the ROLLBACK statement but also for implicit rollbacks.

当 InnoDB 完整回滚一个事务时，该事务设置的所有锁都会被释放。如果事务中的单条 SQL 语句因错误（例如重复键错误）而回滚，该语句设置的锁会保留，而事务仍然保持活动状态。这是因为 InnoDB 以一种无法事后确定哪个锁是由哪个语句设置的格式存储行锁。When InnoDB performs a complete rollback of a transaction, all locks set by the transaction are released. If a single SQL statement within a transaction rolls back as a result of an error, such as a duplicate key error, locks set by the statement are preserved while the transaction remains active. This happens because InnoDB stores row locks in a format such that it cannot know afterward which lock was set by which statement.

如果事务中的SELECT 语句调用了存储函数，而存储函数内的语句失败，则该语句会回滚。如果随后对事务执行了ROLLBACK，则整个事务将回滚。If a SELECT statement within a transaction calls a stored function, and a statement within the stored function fails, that statement rolls back. If ROLLBACK is executed for the transaction subsequently, the entire transaction rolls back.