SQLite database supports a number of SQL commands that can be used to manipulate data in a database. One of these commands is the BEGIN TRANSACTION command.
The BEGIN TRANSACTION command is used to start a transaction in SQLite. A transaction is a series of SQL commands that are executed as a single unit of work. In other words, a transaction is a way of grouping a set of SQL commands together so that they are executed as a single operation. Transactions are used to ensure data integrity, consistency, and recoverability.
Syntax
BEGIN TRANSACTION; --SQL commands COMMIT | ROLLBACK;
When a transaction is started using the BEGIN TRANSACTION command, SQLite begins to record all changes made to the database. These changes are not immediately saved to the disk. Instead, they are recorded in a temporary area called the “rollback journal”. The purpose of the rollback journal is to allow the transaction to be rolled back if necessary. If any errors occur during the execution of the transaction, the entire transaction can be undone by rolling back the changes recorded in the rollback journal.
Once the transaction is completed successfully, it can be committed using the COMMIT command. When a transaction is committed, all changes made to the database during the transaction are saved to the disk. If any errors occur during the commit process, the transaction can be rolled back to its previous state using the ROLLBACK command.
Example
BEGIN TRANSACTION; UPDATE accounts SET balance = balance - 100 WHERE account_id = 15; UPDATE accounts SET balance = balance + 100 WHERE account_id = 51; COMMIT;
In this example, the BEGIN TRANSACTION statement starts a new transaction, which ensures that either all of the updates to the accounts table succeed or none of them do. If any of the updates fail (e.g. due to a constraint violation), the transaction can be rolled back to its original state using the ROLLBACK statement.
The two UPDATE statements inside the transaction update the balances of two different bank accounts. Finally, the COMMIT statement ends the transaction, saving all the changes to the accounts table if they were successful.
In summary, the BEGIN TRANSACTION command is used to start a transaction in SQLite. It ensures data integrity and consistency by grouping a set of SQL commands together as a single unit of work. When a transaction is started, SQLite begins to record all changes made to the database in a temporary area called the rollback journal. The transaction can be committed using the “COMMIT” command or rolled back using the “ROLLBACK” command, depending on the outcome of the transaction.