How to Select multiple queries in PHP to MySQL Using UNION

Описание: Learn how to efficiently fetch multiple records from a MySQL database in PHP using the UNION statement. This guide provides insights into common errors and their solutions.
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This video is based on the question https://stackoverflow.com/q/69712027/ asked by the user 'Saeed' ( https://stackoverflow.com/u/5790653/ ) and on the answer https://stackoverflow.com/a/69712197/ provided by the user 'Devstorm' ( https://stackoverflow.com/u/3105102/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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How to Select Multiple Queries in PHP to MySQL Using UNION

When working with databases, we often need to retrieve data based on different criteria. A common challenge arises when trying to execute multiple SQL queries in PHP, particularly when using MySQL. Many developers stumble upon the issue where running queries in isolation succeeds, but when combined, the execution fails. Let's explore how to effectively select multiple queries in PHP using MySQL and overcome these challenges.

The Problem

You might find yourself in a situation where you want to select records based on multiple IP addresses, as shown in the original code snippet:

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

While this query works flawlessly in MySQL directly, attempting to execute it in PHP produces an error:

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

This error usually indicates that the query did not return a valid result set, meaning your multiple queries were not executed as expected.

Understanding the Solution: Using the UNION Statement

To effectively retrieve results from multiple queries in a single call, you can use the UNION SQL operator. This operator allows you to combine the results of two or more SELECT queries into a single result set, ensuring they can be handled seamlessly in PHP.

Here's the revised code to fetch multiple entries based on different IP addresses:

New Query Structure

Instead of running two queries, you can structure your query as follows:

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

Complete PHP Code Example

With the new query structure, here's how the complete PHP code will look:

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

Key Takeaways

Use UNION: This allows you to combine multiple SELECT statements into a single query, which avoids issues when trying to fetch results from multiple independent queries.

Check for Errors: Always ensure your connection to the database is successful. Handle any errors gracefully to help with debugging.

Combine Results: With UNION, multiple results can be outputted together, making your data retrieval efficient.

By following the steps outlined above, you can effectively manage multiple queries within your PHP code and enhance your application's functionality. Happy coding!