SQL LAST_VALUE with GO statement

29 Sep 2023

In SQL, the LAST_VALUE function is used to retrieve the last value in an ordered window frame within a result set. It comes in handy when you need to access the final value in a specific column based on a particular ordering. The GO statement, on the other hand, is used in SQL Server Management Studio (SSMS) to separate T-SQL batches.

Let’s explore how to use the LAST_VALUE function in conjunction with the GO statement.

Syntax of LAST_VALUE Function

The basic syntax of the LAST_VALUE function is as follows:

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

The expression represents the column or expression from which you want to retrieve the last value. The PARTITION BY clause, if specified, divides the result set into partitions. The ORDER BY clause defines the order within each partition. Lastly, the ROWS BETWEEN clause specifies the window frame that should include all rows from the start of the partition to the end.

Example Usage

Suppose we have a table named Customers with the following columns: CustomerID, CustomerName, and OrderDate. We want to find the last order date for each customer. Here’s how you can accomplish this using the LAST_VALUE function:

SELECT DISTINCT
    CustomerID,
    CustomerName,
    LAST_VALUE(OrderDate) OVER (
        PARTITION BY CustomerID
        ORDER BY OrderDate
        ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING
    ) AS LastOrderDate
FROM
    Customers

In the above example, the PARTITION BY clause divides the result set into partitions based on the CustomerID column. The ORDER BY clause orders the rows within each partition by the OrderDate column in ascending order. The LAST_VALUE function then retrieves the last OrderDate value within each partition. The DISTINCT keyword is used to eliminate duplicate rows from the result set.

Working with GO Statement

The GO statement has no impact on the usage of the LAST_VALUE function. However, it is important to note that the GO statement is not a part of the T-SQL language; it is only recognized by SSMS as a batch separator.

When using the GO statement to execute the above query in SSMS, you would write:

SELECT DISTINCT
    CustomerID,
    CustomerName,
    LAST_VALUE(OrderDate) OVER (
        PARTITION BY CustomerID
        ORDER BY OrderDate
        ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING
    ) AS LastOrderDate
FROM
    Customers
GO

The GO statement here indicates the end of the current batch and executes the query up until that point.

Conclusion

The LAST_VALUE function is a powerful tool in SQL when you need to retrieve the last value in a column within an ordered window frame. By using the PARTITION BY and ORDER BY clauses, you can control the scope of the result set and specify the ordering of the rows. Just keep in mind that the GO statement is used solely as a batch separator within SSMS, allowing you to execute multiple queries in sequence.