使用 BEGIN 和 START TRANSACTION 时 MySQL AUTOCOMMIT 状态

Question

我需要在我的 MySQL 项目中使用事务。但我不确定是否必须使用 mysql_query("SET AUTOCOMMIT=0"); 或不。
我知道我有 2 个选择:

1. 开始
2. 开始交易

我还听说这两项中的一项不需要使用 AUTOCOMMIT = 0。
请帮助我知道什么时候我必须使用 AUTOCOMMIT = 0 实际使用 BEGIN 或 START TRANSACTION？

谢谢。

Answer 1

如 the manual 中所述:

By default, MySQL runs with autocommit mode enabled. This means that as soon as you execute a statement that updates (modifies) a table, MySQL stores the update on disk to make it permanent. The change cannot be rolled back.

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;

With START TRANSACTION, autocommit remains disabled until you end the transaction with COMMIT or ROLLBACK. The autocommit mode then reverts to its previous state.

手册接着说:

To disable autocommit mode explicitly, use the following statement:

SET autocommit=0;

After disabling autocommit mode by setting the autocommit variable to zero, changes to transaction-safe tables (such as those for InnoDB or NDBCLUSTER) are not made permanent immediately. You must use COMMIT to store your changes to disk or ROLLBACK to ignore the changes.

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 5.1.3, “Server System Variables”.

BEGIN and BEGIN WORK are supported as aliases of START TRANSACTION for initiating a transaction. START TRANSACTION is standard SQL syntax and is the recommended way to start an ad-hoc transaction.