How to Fix MySQL Query to Get the Latest Case Number for Unique Face IDs

Details

Description

In this guide, we explain a common MySQL query issue regarding fetching the latest case number for a specific face ID in a patient database. Get step-by-step guidance on how to correct it.
---
This video is based on the question https://stackoverflow.com/q/67148862/ asked by the user 'T THE R' ( https://stackoverflow.com/u/14177036/ ) and on the answer https://stackoverflow.com/a/67149004/ provided by the user 'Tal Rofe' ( https://stackoverflow.com/u/9105207/ ) 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: mysql query does not find the latest record but the first one

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

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
How to Fix MySQL Query to Get the Latest Case Number for Unique Face IDs

When working with databases, especially in healthcare systems, it’s crucial to retrieve the correct and most recent information efficiently. One common issue faced by developers is formulating queries that fetch the latest records effectively. In this guide, we're going to address a specific problem where a MySQL query fails to return the latest case_number for patients with unique face_dev_id values. Let's dive into the details and find the solution.

The Challenge

Consider the following tables in a medical database:

patient: Contains information about patients including unique identifiers and personal details.

patient_case_number: Stores case numbers and associated timestamps for patients.

You need to write a query that, given a specific face_dev_id, retrieves the latest case_number from the patient_case_number table. The original implementation of the query aims to retrieve this, but instead, it retrieves the first case number instead of the latest one. Below is the core of the problem—the query causing the confusion.

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

In this query, due to an ordering by created_at in ascending order and without limiting the inner query effectively, the results do not return the latest case number as required. Let’s analyze how to fix it.

The Solution

Step 1: Change the Order Direction

To fetch the latest records, the important change is to sort the created_at column in descending order. This adjustment allows the query to consider the most recent entries first.

Step 2: Limit the Inner Query

By adding LIMIT 1 to the inner query, we can ensure that only the top result (which is the most recent due to descending order) is taken into consideration.

Revised Query

Here is how the corrected SQL query should look:

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

Conclusion

By simply changing the order of records in your inner query to DESC and applying a LIMIT 1, you can effectively retrieve the most recent case_number associated with a face_dev_id.

Summary Steps:

Modify the ORDER BY clause to sort in descending order (DESC).

Add LIMIT 1 to target only the latest entry.

This adjustment ensures you're working with the latest records in your patient database and resolves the issue effectively. Happy querying!