Скачать или смотреть How to Select Rows from MySQL Based on Conditions in PHP

A guide on how to retrieve rows from multiple related tables in MySQL using PHP, focusing on conditional statements and priority selection.
---
This video is based on the question https://stackoverflow.com/q/73349263/ asked by the user 'ZergRush' ( https://stackoverflow.com/u/8066191/ ) and on the answer https://stackoverflow.com/a/73349884/ provided by the user 'Henry Antona' ( https://stackoverflow.com/u/19760555/ ) 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: Getting a row based on the condition

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 Rows from MySQL Based on Conditions in PHP

In the world of databases, retrieving the right data based on conditions can sometimes feel like solving a puzzle. If you’re trying to fetch specific rows from related tables in MySQL using PHP and you're struggling, don’t worry! In this guide, we will break down the solution to a common problem: selecting entries based on a conditional statement.

The Problem

Imagine you have two tables that are related: an entry table and an entries table. You want to:

Randomly select one entry from the entries table where the corresponding entry has early_finish set to 1 (indicating priority).

If no entries with early_finish = 1 exist, then pick one with early_finish set to 0.

After that, you want to randomly select another entry, but this time ensuring it has a different group_id than the first selected entry.

This might sound easy at first, but without the right approach, it can be tricky.

The Solution

To achieve this, we can use a combination of SQL's JOIN and ORDER BY RAND() clauses along with a CASE statement for our conditions. Let’s break down the solution step-by-step.

Step 1: Setting Up Your SQL Query

Here’s the SQL query that will help you meet your requirements:

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

Step 2: Breakdown of the Query

SELECT Statement: This retrieves the required columns from both tables, including the fought field which we'll update later.

LEFT JOIN: We join the entries table (es) with the entry table (e) on the condition that the parent_id matches the id.

WHERE Clause:

The first condition checks if early_finish is set to 1, but uses a subquery (COUNT) to verify if any entries exist with early_finish as 1.

The second part checks that the fought field remains 0 to ensure only entries that haven’t been selected yet are considered.

ORDER BY RAND(): This randomizes the results so we can select a random entry.

LIMIT 1: Finally, this ensures that we only get one entry as a result.

Step 3: PHP Code Implementation

To execute this SQL query in PHP, you would typically use something like this:

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

Final Selection

After selecting the first entry, if you want to select a second one with a different group_id, you would repeat the process while ensuring to adjust the conditions accordingly.

Conclusion

In this guide, we covered how to select rows based on specific conditions from two related tables in MySQL. By using combinations of JOIN, ORDER BY, and conditional logic, you can efficiently retrieve and manage your data according to your application needs.

With this query structure, you can now prioritize entries based on early_finish effectively. Don't hesitate to adjust the query to better fit your specific dataset and requirements.

Happy coding!