How to roll back in oracle

The rollback operation in Oracle can undo the changes in uncommitted transactions and restore the database to the state before the transaction started. There are two methods of rollback: explicitly rolling back the current transaction using the ROLLBACK statement, or automatically rolling back the transaction when an error occurs through exception handling. Rollback can only undo changes in an uncommitted transaction, and the best practice is to use exception handling to handle errors in the transaction to ensure that the transaction is rolled back correctly when an error occurs.

Oracle rollback: how to undo a transaction

Rollback in Oracle is a database operation used to undo All changes in uncommitted transactions. A transaction is a set of consecutive database operations that either all succeed or all fail. If any operation within the transaction fails, the entire transaction is rolled back, restoring the database to the state it was in before the transaction began.

How to roll back an Oracle transaction

There are two ways to roll back a transaction in Oracle:

• Use the ROLLBACK statement : The ROLLBACK statement is used to explicitly roll back the current transaction. It will undo all changes performed within the transaction.

<code class="sql">ROLLBACK;</code>

• Exception handling: Exception handling can be used to automatically roll back a transaction after an error occurs. Oracle throws an exception when an error occurs in a transaction. If the exception is not handled, the transaction is automatically rolled back.

Example

The following example demonstrates how to use the ROLLBACK statement to roll back an Oracle transaction:

<code class="sql">BEGIN
  -- 开始一个事务
  START TRANSACTION;

  -- 执行一些更新
  UPDATE employees SET salary = salary * 1.10
  WHERE department_id = 10;

  -- 发生错误
  UPDATE employees SET salary = salary * -1 -- 错误：负数工资
  WHERE department_id = 20;

  -- 回滚事务
  ROLLBACK;
END;</code>

In the above example, the first The UPDATE statement executes successfully, but the second UPDATE statement fails due to a negative salary error. The ROLLBACK statement rolls back the entire transaction, undoing all changes from both UPDATE statements.

Note

• Rollback can only undo changes in committed transactions. Committed transactions cannot be rolled back.
• If an error occurs during rollback of a transaction, Oracle will roll back the transaction but will not throw an exception.
• Best practice is to use exception handling to handle errors within a transaction to ensure that the transaction is properly rolled back when an error occurs.

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