SQL LAST_VALUE with EXISTS keyword

28 Sep 2023

In SQL, the LAST_VALUE function is used to obtain the last value in a specified column, based on a specific ordering. The EXISTS keyword, on the other hand, is a logical operator used to determine whether a subquery returns any rows. In this article, we will explore how to use the LAST_VALUE function in combination with the EXISTS keyword in SQL.

Syntax and Usage

The basic syntax of the LAST_VALUE function with the EXISTS keyword is as follows:

SELECT column_name, LAST_VALUE(column_name) OVER (ORDER BY order_column)
FROM table_name
WHERE EXISTS (SELECT 1 FROM subquery);

Here,

column_name is the name of the column from which we want to retrieve the last value.
table_name is the name of the table containing the column.
order_column is the column used for ordering the rows.
subquery is a SQL query that returns a result set.

Example

Let’s say we have a table called sales with the following structure:

sale_id	sale_date	amount
1	2021-01-01	100
2	2021-01-02	150
3	2021-01-03	200
4	2021-01-04	250
5	2021-01-05	300

Now, we want to retrieve the last value of the amount column for the sales made on or after a specific date.

SELECT sale_date, LAST_VALUE(amount) OVER (ORDER BY sale_date)
FROM sales
WHERE EXISTS (SELECT 1 FROM sales WHERE sale_date >= '2021-01-03');

In the above example, we are selecting the sale_date column and using the LAST_VALUE function to get the last value of the amount column based on the ordering of sale_date. We are also using the EXISTS keyword to filter out sales before the date '2021-01-03'.

The result of the above query will be:

sale_date	last_value
2021-01-03	300
2021-01-04	300
2021-01-05	300

As you can see, the LAST_VALUE function retrieves the last value of the amount column and repeats it for each row, as specified by the ordering. The EXISTS keyword ensures that only rows with a sale_date on or after '2021-01-03' are included.

Conclusion

In this article, we have learned how to use the LAST_VALUE function with the EXISTS keyword in SQL. By combining these two, we can retrieve the last value of a column based on a specific ordering, while also filtering out rows using a subquery. This can be useful in scenarios where we want to analyze or display the most recent data from a table.

#sql #lastvalue #exists