In SQL, the LAST_VALUE function is used to retrieve the last value in a specified column within a partition of a result set. When used in conjunction with the CURSOR statement, it allows for efficient and iterative retrieval of data.

Understanding Cursors

A cursor is a database object that enables traversal (moving through records) and manipulation of result sets in a row-by-row manner. Cursors are particularly useful when dealing with large datasets or when performing complex data operations.

Using the LAST_VALUE Function with CURSOR

To demonstrate the usage of LAST_VALUE with CURSOR, let’s consider a scenario where we have a table called employees with columns employee_id, first_name, last_name, and salary. Our goal is to retrieve the last salary for each employee.

Here’s an example of how to achieve this using SQL Server:

-- Declare the cursor
DECLARE emp_cursor CURSOR FOR
SELECT employee_id, salary
FROM employees
ORDER BY employee_id;

-- Declare variables to store the values
DECLARE @employee_id INT, @salary DECIMAL(10, 2), @last_salary DECIMAL(10, 2);

-- Open the cursor
OPEN emp_cursor;

-- Fetch the first row
FETCH NEXT FROM emp_cursor INTO @employee_id, @salary;

-- Iterate through the cursor
WHILE @@FETCH_STATUS = 0
BEGIN
    -- Assign the current salary to the last salary variable
    SET @last_salary = LAST_VALUE(@salary) OVER (ORDER BY @employee_id ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING);

    -- Output the result
    PRINT 'Employee ID: ' + CAST(@employee_id AS NVARCHAR(10)) + ' - Last Salary: ' + CAST(@last_salary AS NVARCHAR(10));

    -- Fetch the next row
    FETCH NEXT FROM emp_cursor INTO @employee_id, @salary;
END

-- Close and deallocate the cursor
CLOSE emp_cursor;
DEALLOCATE emp_cursor;

In this example, we declare a cursor called emp_cursor and select the employee_id and salary from the employees table, ordering the result set by employee_id. We declare variables to store the values returned from the cursor.

We then open the cursor and fetch the first row into the declared variables. Inside the loop, we use the LAST_VALUE function to retrieve the last salary by ordering the rows by employee_id, ensuring that it includes all rows from the beginning till the end.

Finally, we print the result and fetch the next row until there are no more rows. We close and deallocate the cursor at the end to release resources.

Conclusion

Using the LAST_VALUE function with the CURSOR statement in SQL allows you to efficiently retrieve the last value in a specified column within a partition of a result set. Cursors offer a convenient way to traverse and manipulate data row by row. By combining these two concepts, you can perform complex data operations and analyze valuable insights from your database.