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Introduction
Reports with revenue in categories
Revenue in time periods for selected categories
Summary

## Instruction

Good! Let's get started. There are two queries which we can use for total revenue as follows:

SELECT SUM(amount) AS total_revenue FROM orders;

Or:

SELECT SUM(amount) AS total_revenue FROM order_items;

Now, let's say we want to show the history-to-date revenue for various categories:

category_name total_revenue
Seafood 131261.75
Meat/Poultry 163022.37
Condiments 106047.11

Such a report can help us discover which product categories are more profitable. In this case, we can only use the second query (the one with the order_items table). Take a look:

SELECT
category_name,
SUM(amount) AS total_revenue
FROM order_items oi
JOIN products p
ON oi.product_id = p.product_id
JOIN categories c
ON p.category_id = c.category_id
GROUP BY category_name;


This query is a bit more complicated because we had to join order_items with products and categories to get the category names used in the report.

## Exercise

Run the template query and see how it generates a row with the history-to-date revenue for each category.