Скачать или смотреть How to Select the First Largest Value Using TOP 1 in MySQL

Learn how to effectively extract the first largest value from a MySQL table using `TOP 1`, illustrated with practical examples and solutions.
---
This video is based on the question https://stackoverflow.com/q/66034594/ asked by the user 'Wrapper' ( https://stackoverflow.com/u/20390023/ ) and on the answer https://stackoverflow.com/a/66035742/ provided by the user 'Bill Karwin' ( https://stackoverflow.com/u/20860/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: Select first largest value using TOP 1 in MySQL?

Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l...
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license.

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
How to Select the First Largest Value Using TOP 1 in MySQL

When working with MySQL databases, it’s common to encounter scenarios where you need to retrieve a specific record based on comparative values within the same column. In this guide, we will explore a problem related to selecting the first largest value using TOP 1 in MySQL, and we’ll provide a clear, step-by-step solution to help you implement this in your own projects.

The Problem

Suppose you have a table named pricelist with two columns: pricelist_id and valid_from, as shown below:

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

The values in the valid_from column are timestamps generated in milliseconds since January 1, 1970, representing specific dates. Your goal is to find the pricelist_id that corresponds to the largest valid_from value that is lower than or equal to a provided value. For instance:

If the provided timestamp is for Jan 18th (1610924400000), the expected output is 3.

If the provided timestamp is for Jan 16th 17:15:00 (1610813700000), the expected output is 2.

If the timestamp represents Jan 25th (1611529200000), the output should again be 3.

The Solution

We have a couple of approaches to achieve this, depending on whether your pricelist_id maintains the same order as valid_from. Here’s how you can implement both methods in SQL:

Method 1: Using MAX() with ORDER BY

If you can ensure that pricelist_id is in the exact same sort order as valid_from, you can use the MAX() function in your query, as follows:

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

Explanation:

MAX(p.pricelist_id) - This retrieves the maximum pricelist_id that meets the condition.

(p.valid_from + 0) <= some_passed_value - This condition filters records based on the provided timestamp.

ORDER BY p.valid_from DESC - Sorting in descending order helps in finding the maximum easily.

Method 2: Using LIMIT

If you cannot guarantee the sort order, a more reliable approach is to use the LIMIT clause along with ORDER BY:

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

Explanation:

This query selects the pricelist_id directly, limiting the result to just one record after it orders the filtered results by valid_from in descending order.

By using LIMIT 1, you ensure that you only retrieve the first record that meets your criteria, which simplifies your output.

Conclusion

Selecting the first largest value in MySQL can be approached in a couple of different ways. Depending on your database structure and the guarantees you have about the order of your data, you can utilize either the MAX() function or the LIMIT clause effectively. By understanding both methods, you now have the flexibility to choose the best approach for your specific use case.

Armed with these insights, you should be able to tackle similar challenges whenever you face them. Happy querying!