Transaction in SQL

Описание: A transaction in SQL is a sequence of one or more operations that are executed as a single unit of work. Transactions ensure that the database remains consistent and reliable even in the event of errors, crashes, or interruptions. They adhere to the ACID properties (Atomicity, Consistency, Isolation, Durability), which guarantee the integrity and reliability of data.

Key Characteristics of Transactions:
Atomicity:

Ensures that all parts of a transaction are completed successfully. If any part fails, the entire transaction is rolled back, leaving the database in its original state.
Consistency:

Guarantees that a transaction brings the database from one valid state to another, maintaining all rules, constraints, and relationships defined in the database.
Isolation:

Ensures that transactions occur independently without interfering with each other. Intermediate states of a transaction are not visible to other concurrent transactions.
Durability:

Once a transaction is completed and committed, its changes are permanent, even in the event of a system failure.
Common Operations in Transactions:
Start a Transaction:

A transaction begins when a series of operations are grouped together for execution. This ensures that all included operations are treated as a single unit.
Commit a Transaction:

When a transaction is successfully completed, its changes are saved permanently to the database. This marks the transaction as complete.
Rollback a Transaction:

If an error occurs or a condition is not met, the transaction can be canceled, undoing all changes made during the transaction.
Savepoints in Transactions:

Savepoints allow you to set specific points within a transaction that you can return to if needed. This is useful for rolling back only part of a transaction without undoing all changes.
Set Transaction Properties:

Transactions can be configured with specific properties, such as the level of isolation, to control how they interact with other transactions.
Real-World Examples:
Banking Systems:

Transferring money between accounts involves multiple operations like debiting one account and crediting another. If one operation fails, the entire transfer must be rolled back.
E-Commerce:

Placing an order might involve checking inventory, deducting stock, and updating the customer’s order details. These operations must be handled as a single transaction to avoid inconsistencies.
Inventory Management:

When adjusting inventory levels, a transaction ensures that stock counts remain accurate, even if multiple users are updating the system simultaneously.
Benefits of Transactions:
Data Integrity: Transactions ensure that data remains accurate and consistent.
Error Recovery: If something goes wrong, transactions provide a way to undo partial changes and restore the original state.
Concurrent Access Control: Transactions allow multiple users to work on the database simultaneously without conflicts.
Reliability: Changes are permanent and reliable once a transaction is completed.
Transactions are a cornerstone of database management, offering a structured way to manage changes and maintain the reliability of critical data.


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