In SQL, the LAST_VALUE function is used to return the last value of an expression within a specified partition. It is often used in conjunction with the ROLLBACK statement to handle cases where we need to undo changes made by a particular operation.

Syntax

The syntax for using LAST_VALUE with ROLLBACK is as follows:

LAST_VALUE (expression) OVER (
  [PARTITION BY column]
  ORDER BY column
  ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING
)

Example

Consider a scenario where we have a table named employees with the following columns: employee_id, employee_name, and salary. We want to update the salary of all employees to the maximum salary value within their respective departments. However, we want to make sure that if the update fails for any reason, we can rollback the changes.

Here’s how we can achieve this using LAST_VALUE and ROLLBACK:

BEGIN TRANSACTION;

UPDATE employees
SET salary = (
  SELECT LAST_VALUE(salary) OVER (
    PARTITION BY department_id
    ORDER BY salary DESC
    ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING
  ) AS max_salary
  FROM employees
)
WHERE EXISTS (
  SELECT 1
  FROM employees
  WHERE department_id = employees.department_id
  GROUP BY department_id
  HAVING COUNT(*) > 1
);

IF @@ERROR <> 0
  ROLLBACK TRANSACTION;
ELSE
  COMMIT TRANSACTION;

In this example, the LAST_VALUE function is used to retrieve the maximum salary value within each department. The UPDATE statement then updates the salary column of the employees table with the calculated maximum salary.

If an error occurs during the update operation, the ROLLBACK statement is executed to undo the changes made by the UPDATE statement. Otherwise, the changes are committed using the COMMIT statement.

By using LAST_VALUE with ROLLBACK, we can ensure that our database remains in a consistent state even if an error occurs during the data manipulation process.

#SQL #ROLLBACK