Rollback in SQL | Structured Query Language

In SQL (Structured Query Language), the ROLLBACK statement is used to undo changes made in a transaction that has not been committed to the database. A transaction is a series of database operations that are treated as a single unit of work. The ROLLBACK statement allows you to undo all changes made in that transaction and return the database to its previous state.

The basic syntax of the ROLLBACK statement is as follows:

```
ROLLBACK;
```

The ROLLBACK statement does not have any parameters or arguments. It simply undoes all changes made in the current transaction and returns the database to its previous state.

For example, if you have a transaction that inserts a new record into a table, updates an existing record, and deletes another record, you can use the following SQL statements to execute the transaction and then roll back the changes:

```
START TRANSACTION;
INSERT INTO mytable (col1, col2) VALUES ('value1', 'value2');
UPDATE mytable SET col1 = 'newvalue1' WHERE col2 = 'value2';
DELETE FROM mytable WHERE col1 = 'oldvalue1';
ROLLBACK;
```

The START TRANSACTION statement starts the transaction, and the ROLLBACK statement undoes all changes made in that transaction and returns the database to its previous state.

Note that if you execute a COMMIT statement before executing the ROLLBACK statement, the changes made in the transaction will be permanently saved to the database and cannot be rolled back.