Скачать или смотреть How to Generate a Lower Limit from an Upper Limit in SQL Using T-SQL

Learn how to calculate the lower limit based on an upper limit in a SQL dataset using the T-SQL `LAG()` function for effective data manipulation.
---
This video is based on the question https://stackoverflow.com/q/72983042/ asked by the user 'Kiko Frias' ( https://stackoverflow.com/u/19283768/ ) and on the answer https://stackoverflow.com/a/72983127/ provided by the user 'Tim Biegeleisen' ( https://stackoverflow.com/u/1863229/ ) 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: SQL to show lower limit provided the upper limit

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.
---
Introduction

Have you ever found yourself in a situation where you need to derive a lower limit from an existing upper limit in your SQL databases? This is quite common, especially when you're working with ranges or thresholds in a dataset. In this guide, we will explore how to use T-SQL to achieve that when provided with a sample dataset.

The Problem

Let's say you have the following dataset with rank and Upper_limit values:

rankUpper_limit12.112334.548.159.7You want to transform this dataset to include a new column Lower_limit, such that each Lower_limit is equal to the Upper_limit of the previous rank. For the first row, since there is no previous value, the Lower_limit would default to 0. The desired output should be:

rankLower_limitUpper_limit102.1122.113334.544.58.158.19.7The Solution

To achieve this transformation, we can utilize the powerful analytic function LAG() in T-SQL. The LAG() function allows us to access data in the previous row while querying the dataset, which makes it perfect for calculating the Lower_limit based on the Upper_limit of the previous rank.

SQL Query Using LAG()

Here's how you can write the SQL query to perform the transformation:

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

Breaking Down the Query

SELECT Statement: We begin by selecting the rank and Upper_limit which we already have in our dataset.

Using LAG():

The first argument is Upper_limit, indicating the value from the previous row that we're interested in.

The second argument 1 tells SQL to look back one row.

The third argument 0 sets the default value for the first row when there’s no previous value.

OVER (ORDER BY [rank]): This specifies how we want the rows to be ordered while applying the LAG() function. In this case, we want to order them by rank, which is essential to maintain the correct sequence.

ORDER BY Clause: Finally, we order the results by rank to ensure they are displayed in the intended order.

Conclusion

By using the LAG() function in T-SQL, we can elegantly derive lower limits from existing upper limits in a dataset with minimal code. This approach not only enhances data analysis but also increases efficiency when dealing with large datasets.

Feel free to implement this in your SQL environment and modify it according to your data needs. Happy querying!