begin end usage in sql

In SQL, BEGIN and END are used as transaction boundary markers to ensure the atomicity, durability, and isolation of operations. BEGIN starts a transaction and END commits or rolls back the transaction. 1. BEGIN starts a transaction. 2. Perform an operation (insert, update, etc.). 3. COMMIT commits the transaction and makes the changes permanent. 4. ROLLBACK rolls back the transaction and undoes the changes.

Usage of BEGIN and END in SQL

In SQL, BEGIN and END are used as transaction boundary markers . A transaction is a series of atomic operations that either all succeed or all fail. BEGIN and END are used to group these operations together to ensure atomicity.

Usage

The BEGIN statement starts a transaction, and the END statement commits or rolls back the transaction:

<code class="sql">BEGIN;  -- 开始事务

-- 执行操作...

COMMIT;  -- 提交事务（使更改永久化）

-- 或者

ROLLBACK;  -- 回滚事务（撤消更改）</code>

Atomicity

The atomicity of a transaction means that either all operations succeed or all operations fail. If an error occurs during a transaction, the ROLLBACK statement undoes all operations that have been performed, restoring the database to the state it was in when the transaction began.

Persistence

The COMMIT statement makes changes within a transaction permanent. Once the COMMIT statement is executed, these changes are persisted in the database, even if a failure occurs or the application is shut down.

Isolation

Transactions also provide isolation, which means that changes in one transaction are not visible to other transactions until the COMMIT statement is executed. This helps prevent concurrent access from causing data inconsistency.

Example

The following example shows the use of BEGIN and END in SQL:

<code class="sql">BEGIN;

INSERT INTO customers (name, email) VALUES ('John Doe', 'john.doe@example.com');

UPDATE customers SET email = 'john.doe@new-example.com' WHERE id = 1;

COMMIT;</code>

In this example, the BEGIN statement starts a transaction, and then Performs two operations: inserting a new customer and updating an existing customer's email. The COMMIT statement commits the transaction, making the changes permanent. If an error occurs during an insert or update, the ROLLBACK statement rolls back both operations.

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