Querying Devices in SQL: Select All Devices Ordered from Most Expensive to Cheapest

Описание: Learn how to use SQL to select and order devices by price in descending order with this easy-to-follow guide.
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This video is based on the question https://stackoverflow.com/q/64638450/ asked by the user 'Sseis Esime Zacatenco' ( https://stackoverflow.com/u/13030154/ ) and on the answer https://stackoverflow.com/a/64638541/ provided by the user 'Ken Lee' ( https://stackoverflow.com/u/11854986/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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How to Select All Devices Ordered from Most Expensive to Cheapest

In the world of data management, querying databases efficiently is essential, especially when you need specific insights like ordering products by price. If you’re working with a database that contains various devices — such as printers, laptops, and PCs — you may want to retrieve them arranged from the most expensive to the cheapest. In this guide, we’ll walk you through the steps to create the right SQL query to achieve this goal.

Understanding the Problem

Recently, there was a common question from a user trying to run an SQL query to get all devices ordered from the most expensive to the cheapest. Here is an outline of the problematic SQL command they attempted:

[[See Video to Reveal this Text or Code Snippet]]

Unfortunately, they encountered an error stating missing expression. This error usually means that there’s something wrong with the syntax or structure of the query.

Why It Didn't Work

The user's query failed for a couple of reasons:

Table Relationship: The tables (Printer, Laptop, and PC) are not joined based on any common key. When querying multiple tables without a relationship defined, the database has trouble understanding how to collate the information.

Incorrect Order Direction: The user intended to order the results by price in a descending fashion, but they used ASC (ascending order) instead of DESC (descending order).

Crafting the Right Query

To resolve these issues and get the desired output, we need to strategically combine the data from these separate tables and order them correctly. Here’s how you can do this:

Using UNION to Combine Tables

Since these tables do not have a direct relationship, we will use the UNION operator. This operator allows you to combine the results of two or more SELECT statements. Here’s the correct SQL query you should use:

[[See Video to Reveal this Text or Code Snippet]]

Breaking Down the Query

SELECT model, price: This part of the query selects the columns you want to retrieve, specifically the model and price of each device.

FROM printer, laptop, and pc: Each SELECT command targets a different table where the device data is stored.

UNION: This keyword combines the result sets of the individual queries into one single result set.

ORDER BY price DESC: Finally, this sorts all the combined results by price in descending order, meaning the most expensive items appear first.

Conclusion

By using the UNION operator along with proper ordering, you can efficiently retrieve and display all devices from most to least expensive. This approach is particularly useful when dealing with multiple tables that contain comparable data, such as our example of printers, laptops, and PCs.

Now you can confidently retrieve your device listings in the order you need, making your database interactions smoother and more effective. Happy querying!