In this blog post, we will explore how to use the LAST_VALUE() function in SQL along with the UNION statement. We will dive into the syntax of the LAST_VALUE() function, provide examples of its usage, and discuss how it can be used in combination with the UNION statement to solve specific scenarios.

Syntax of the LAST_VALUE() Function

The syntax for the LAST_VALUE() function is as follows:

LAST_VALUE(expression) OVER (PARTITION BY column ORDER BY column [ROWS {UNBOUNDED PRECEDING | n PRECEDING | CURRENT ROW}])

Where:

• expression is the column or expression for which you want to retrieve the last value.
• PARTITION BY column specifies the column used to group the rows.
• ORDER BY column specifies the column used to determine the order of the rows.
• ROWS {UNBOUNDED PRECEDING | n PRECEDING | CURRENT ROW} defines the window frame within which the LAST_VALUE() operates. It specifies the range of rows to consider.

Examples

Let’s consider a simple example where we have a “Sales” table with columns “Product”, “Date”, and “Quantity”. We want to retrieve the last quantity sold for each product.

SELECT DISTINCT
   Product,
   LAST_VALUE(Quantity) OVER (PARTITION BY Product ORDER BY Date) AS LastQuantity
FROM
   Sales;

In the above example, the LAST_VALUE() function is used to retrieve the last quantity sold for each product by ordering the rows based on the “Date” column.

Using LAST_VALUE() with UNION Statement

The UNION statement combines the result of multiple SELECT statements into a single result set. We can use the LAST_VALUE() function in combination with the UNION statement to get the last values from different tables or queries.

Consider the following example where we have two tables “Table1” and “Table2” with similar columns “ID” and “Value”. We want to retrieve the last value among both tables for each ID.

SELECT DISTINCT
   ID,
   LAST_VALUE(Value) OVER (PARTITION BY ID ORDER BY ID) AS LastValue
FROM
   (
      SELECT ID, Value FROM Table1
      UNION ALL
      SELECT ID, Value FROM Table2
   ) AS CombinedTables;

In the above example, we first combine the rows from both tables using the UNION statement. Then, we use the LAST_VALUE() function to get the last value for each ID by ordering the rows based on the ID column.

Conclusion

The LAST_VALUE() function in SQL provides a convenient way to retrieve the last value of a specified column within a window frame. By combining it with the UNION statement, you can obtain the last values from multiple tables or queries. We hope this blog post provided you with a clear understanding of how to use the LAST_VALUE() function with the UNION statement in SQL.

#SQL #LAST_VALUE #UNION