LAST_VALUE

The LAST_VALUE function in Oracle is an analytic function that returns the last value in a specified window of rows, based on the ordering defined by the ORDER BY clause. Similar to FIRST_VALUE, it allows you to retrieve the value from the last row within a specified window or partition of rows without needing to perform self-joins or subqueries.

Here’s a detailed overview of the LAST_VALUE function in Oracle:

 

1. What is the LAST_VALUE Function?

The LAST_VALUE function returns the value of the last row in a window or partition, as defined by the ORDER BY clause. This function helps you fetch the last value from a set of rows, which can be useful for trend analysis, comparing the first and last values in a sequence, or evaluating the final state in a time series.

 

2. Basic Syntax of LAST_VALUE

LAST_VALUE(expression)

    OVER (PARTITION BY partition_expression ORDER BY order_expression ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING)

• expression: The column or expression whose value you want to retrieve from the last row.
• PARTITION BY (optional): Divides the result set into partitions, applying the LAST_VALUE function to each partition separately.
• ORDER BY: Specifies the order in which rows are processed to determine which is considered the "last row."
• ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING: Ensures that the window includes all rows in the partition for accurate computation of the last value. Without this clause, LAST_VALUE might behave unexpectedly as the window may be restricted.

 

3. How Does LAST_VALUE Work?

The LAST_VALUE function operates over a window of rows. It evaluates the rows in the order defined by the ORDER BY clause and returns the value of the last row in that ordered window. The window can be partitioned into groups, allowing the LAST_VALUE function to compute the last value within each partition separately.

For example, if you are analyzing sales data across different regions, you can get the last sale for each region (ordered by sale date) without manually filtering or subsetting the data.

 

4. Example 1: Basic Usage of LAST_VALUE

Consider the following Sales table:

Salesperson	SalesAmount	SaleDate
John	500	2025-01-01
Alice	600	2025-01-02
Bob	450	2025-01-03
Carol	700	2025-01-04

To get the last sales amount based on the sale date:

SELECT Salesperson, SaleDate, SalesAmount,

       LAST_VALUE(SalesAmount) OVER (ORDER BY SaleDate ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING) AS Last_SalesAmount

FROM Sales;

Result:

Salesperson	SaleDate	SalesAmount	Last_SalesAmount
John	2025-01-01	500	700
Alice	2025-01-02	600	700
Bob	2025-01-03	450	700
Carol	2025-01-04	700	700

• Last_SalesAmount shows the last SalesAmount based on the SaleDate, which is 700 for the latest sale on 2025-01-04. This value is repeated for all rows, as it is the last value in the ordered result set.

 

5. Example 2: Using LAST_VALUE with PARTITION BY

You can partition the data into different groups and apply the LAST_VALUE function to each partition. For instance, if you want to get the last sales amount for each region:

SELECT Salesperson, Region, SaleDate, SalesAmount,

       LAST_VALUE(SalesAmount) OVER (PARTITION BY Region ORDER BY SaleDate ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING) AS Last_SalesAmount

FROM Sales;

Result:

Salesperson	Region	SaleDate	SalesAmount	Last_SalesAmount
John	East	2025-01-01	500	600
Alice	East	2025-01-02	600	600
Bob	West	2025-01-03	450	700
Carol	West	2025-01-04	700	700

• The Last_SalesAmount is calculated separately for each region. For the East region, the last sale is 600, and for the West region, the last sale is 700.

 

6. Using LAST_VALUE with a Default Value

You can specify a default value to be used if there are no rows in the partition or window. Here's how you can provide a default value:

SELECT Salesperson, SaleDate, SalesAmount,

       LAST_VALUE(SalesAmount, 0) OVER (ORDER BY SaleDate ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING) AS Last_SalesAmount

FROM Sales;

Result:

Salesperson	SaleDate	SalesAmount	Last_SalesAmount
John	2025-01-01	500	700
Alice	2025-01-02	600	700
Bob	2025-01-03	450	700
Carol	2025-01-04	700	700

• In this case, since the function is applied over all rows with the specified sorting, no default value is needed because the data contains all relevant rows.

 

7. Window Frame Specification

By default, LAST_VALUE is computed over the entire partition when using ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING. This ensures that all rows are considered for determining the last value. However, if the frame specification is not set to include all rows, Oracle may return the last value within the current window frame, not the entire partition.

You must always specify the frame when you want the correct result across the whole partition or window.

 

8. Example 3: Using LAST_VALUE in Time Series Analysis

The LAST_VALUE function is commonly used in time series analysis to evaluate the last recorded value in a sequence. Here's an example with sales data:

SELECT Salesperson, SaleDate, SalesAmount,

       LAST_VALUE(SalesAmount) OVER (ORDER BY SaleDate ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING) AS Last_SalesAmount

FROM Sales

WHERE SaleDate BETWEEN '2025-01-01' AND '2025-01-04';

This will provide you with the last sales amount in the dataset based on the SaleDate ordering.

 

9. When Should I Use LAST_VALUE?

You should use the LAST_VALUE function in scenarios where you need to retrieve the last value in a result set or partition:

• Trend analysis: To compare the final state of a time series.
• Final entries: When you need to extract the last value from a group or ordered sequence.
• Calculating the latest value: For time-based data, like sales figures or stock prices, where the last value is important.

 

10. Performance Considerations

• Windowing: Like other window functions, LAST_VALUE can slow down performance when applied to large datasets, especially when the window spans the entire dataset. Ensure efficient use of indexes on columns used in ORDER BY and PARTITION BY.
• Sorting: Proper indexing on the columns used for sorting (like date columns) can improve performance.

 

11. Comparison with FIRST_VALUE

• FIRST_VALUE returns the first value in the window, while LAST_VALUE returns the last value.
• Both functions can be used with PARTITION BY and ORDER BY to control the window and order in which rows are considered.

 

Conclusion

The LAST_VALUE function is a useful tool for retrieving the last value from a result set or partition in Oracle. It is particularly helpful in time series analysis, trend analysis, and when comparing the first and last values of a dataset. Understanding how to use the ROWS BETWEEN clause effectively is key to getting correct results, especially when working with partitions and ordered sets of rows.