Скачать или смотреть Solving the Substring Query Returning Null Issue in MySQL

Learn how to extract usernames from Facebook profile links in your MySQL database effectively with this comprehensive guide.
---
This video is based on the question https://stackoverflow.com/q/65601405/ asked by the user 'Nick' ( https://stackoverflow.com/u/14932467/ ) and on the answer https://stackoverflow.com/a/65601573/ provided by the user 'RiggsFolly' ( https://stackoverflow.com/u/2310830/ ) 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: Substring Query returning null

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.
---
Understanding the Substring Query Issue

When working with databases, especially those that handle user profiles, it is common to encounter issues related to string manipulation. One such problem arises with the extraction of specific segments from URLs. In this post, we will tackle a common issue faced by many MySQL users: a substring query that returns null.

Imagine you have a column in your database that stores Facebook profile links, such as   / profilename  . You want to extract just the username profilename but run into a problem where your query returns no results.

The Problem Statement

You tried using the following SQL query to extract the username from the Facebook URL:

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

Upon executing this query, you found it returned an empty result. What went wrong?

Breaking Down the Original Query

The initial approach you took was:

FROM users: This specifies the table from which you're trying to retrieve data.

SUBSTRING_INDEX(facebook_link, 'm/', -1): This function aims to extract everything after the last occurrence of m/ in the URL, but it seems to not be giving the expected output.

The main issue here is that you used the WHERE clause to filter the results instead of manipulating the selected data.

The Solution Explained

To properly get the username from the Facebook link, you need to modify your SQL query as follows:

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

Breaking It Down

SUBSTRING_INDEX: This function divides the string based on a delimiter. In this case, we're separating the URL at com/.

The -1 argument means we want everything after the last instance of com/.

AS facebook_link: This part renames the output of the SUBSTRING_INDEX for better readability.

By using this approach, the query directly retrieves and displays the username instead of attempting to filter on an operation that could not be executed correctly.

Removing the Trailing Slash

In most cases, the extracted result may still have a trailing slash (/) that you might want to remove. To do so, you can use the TRIM function in conjunction with your existing query:

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

Explanation of TRIM

TRIM(TRAILING '/' FROM ...): This function is used to remove characters specified (in this case, a trailing slash) from the end of the extracted string.

Conclusion

In summary, resolving the issue of a substring query returning null requires correctly structuring your SQL statements to manipulate string data accurately. Adjusting your query by removing the WHERE clause and using the right string functions will yield the desired username from Facebook profile links.

Try implementing this solution in your database, and you should see immediate results!