In SQL, the LAST_VALUE function is used to return the last value within a specific window frame. It can be handy in scenarios where you need to retrieve the last value of a column based on a specific ordering.

In this blog post, we will explore how to use the LAST_VALUE function in conjunction with the TRUNCATE statement to achieve our desired result.

The TRUNCATE Statement

The TRUNCATE statement is a DDL (Data Definition Language) statement used to remove all the records from a table or a specified partition of a table. Unlike the DELETE statement, TRUNCATE does not log individual row deletions, making it faster and less resource-intensive. However, TRUNCATE is non-recoverable, meaning that once executed, there is no going back.

Syntax of LAST_VALUE Function

The LAST_VALUE function can be used in a SELECT statement to retrieve the last value of a column based on a specific ordering. The syntax for the LAST_VALUE function is as follows:

LAST_VALUE ( expression ) OVER (
    [ PARTITION BY partition_expression ]
    ORDER BY sort_expression
    [ ROWS BETWEEN { UNBOUNDED PRECEDING | n PRECEDING } AND CURRENT ROW ]
)

• expression: The column or expression for which we want to retrieve the last value.
• PARTITION BY: Optional clause used to divide the result set into partitions.
• ORDER BY: The column or expression by which the result set is ordered, determining which value is considered the last.
• ROWS BETWEEN: Optional clause used to specify the window frame within which to evaluate the LAST_VALUE.

Usage of LAST_VALUE with TRUNCATE Statement

Now, let’s see an example of how we can use the LAST_VALUE function with the TRUNCATE statement.

Consider the following sample table named employees:

To remove all the records from the table except the row with the highest salary, we can use the following SQL query:

TRUNCATE TABLE employees 
EXCEPT 
SELECT * FROM (
  SELECT *, LAST_VALUE(salary) OVER (ORDER BY salary) AS last_salary
  FROM employees
) AS subquery 
WHERE salary < last_salary;

In this query, we first use the LAST_VALUE function to find the last (highest) salary from the employees table. Then, we use a subquery to compare each row’s salary with the last_salary. Finally, we use the TRUNCATE statement to delete the rows that don’t meet the condition.

#SQL #LAST_VALUE #TRUNCATE

By combining the power of the LAST_VALUE function and the TRUNCATE statement, you can efficiently delete specific rows from a table while retaining the one with the highest value based on a particular column.