In SQL, the LAST_VALUE function is used to retrieve the last value in a sequence of rows, based on a specified order. This function can be especially useful when combined with a JOIN clause, allowing us to retrieve relevant information from multiple tables.

Syntax

The syntax for using LAST_VALUE with a JOIN clause is as follows:

SELECT column1, column2, ...
FROM table1
JOIN table2 ON table1.columnX = table2.columnY
WHERE <condition>
ORDER BY columnZ
OVER (PARTITION BY partition_column ORDER BY order_column)

Here, table1 and table2 represent the two tables being joined, columnX and columnY are the columns used for joining the tables, <condition> specifies any additional filtering criteria, and columnZ is the column used for ordering the result set.

Example

Consider two tables: orders and customers. We want to retrieve the last order placed by each customer, along with customer details. Here’s an example using the LAST_VALUE function with a JOIN clause:

SELECT customers.customer_id, customers.name, orders.order_id, orders.order_date
FROM customers
JOIN (
    SELECT order_id, customer_id, order_date,
           LAST_VALUE(order_id) OVER (PARTITION BY customer_id ORDER BY order_date) AS last_order_id
    FROM orders
) AS last_orders ON customers.customer_id = last_orders.customer_id AND orders.order_id = last_orders.last_order_id

In this example, we first select the order_id, customer_id, order_date, and the last order_id using the LAST_VALUE function within a subquery. Then, we perform the JOIN between the customers table and the subquery results, matching on the customer_id and last_order_id columns.

By using the LAST_VALUE function with the JOIN clause, we can easily retrieve the last order placed by each customer, along with the corresponding customer details.

#SQL #JOIN