Let’s consider a database scenario with two tables: orders and order_items. The orders table contains information about the orders, such as order ID and customer ID, while the order_items table contains information about the items in each order, such as item ID, order ID, and quantity.

To calculate the sum of the quantities for all the items in each order, we can use the SUM function along with the JOIN clause. Here’s an example of how to write the SQL query for it:

SELECT o.order_id, SUM(oi.quantity) AS total_quantity
FROM orders o
JOIN order_items oi ON o.order_id = oi.order_id
GROUP BY o.order_id;

In the above query, we are selecting the order_id from the orders table and calculating the sum of the quantity column from the order_items table using the SUM function.

The JOIN condition specifies how the two tables are related, in this case, matching the order_id column from both tables. The GROUP BY clause groups the result by the order_id, which allows us to calculate the sum for each order.

The result of this query will provide the order ID along with the total quantity of items in each order.

By using joins and the SUM function, you can easily perform calculations on related data from multiple tables in SQL. It’s a powerful way to aggregate data and extract valuable insights from your database.

#SQL #Join #Sum