Скачать или смотреть How to Fetch Multiple Values from a Table Based on a Foreign Key in PHP/MySQL

Learn how to efficiently fetch multiple values from a MySQL table based on a foreign key relationship using PHP. This guide covers data structure, querying techniques, and practical code examples.
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This video is based on the question https://stackoverflow.com/q/65367011/ asked by the user 'pal deepak' ( https://stackoverflow.com/u/14853526/ ) and on the answer https://stackoverflow.com/a/65367581/ provided by the user 'GMB' ( https://stackoverflow.com/u/10676716/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Fetching Multiple Values from a Table Based on a Foreign Key in PHP/MySQL

In the world of database management, one common challenge developers face is fetching multiple values from a table based on a foreign key relationship. If you're working with MySQL and PHP, this post will guide you through a scenario with two tables and how to efficiently retrieve the necessary data.

The Problem

Imagine you have two related tables in your database:

Table 1: Contains various categories and their associated amounts.

Table 2: Contains group names linked to one or more payroll categories.

Example Table Structures

Table 1:

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

Table 2:

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

Your task is to fetch the sum of amounts from Table 1 based on the payroll categories stored in Table 2. In this case, you’re looking at a string of category codes like PF,HM,BP,TX that you need to process.

The Solution

Rather than sticking with the original data model, which can be inefficient, an ideal scenario would involve restructuring your tables to properly relate categories and groups. However, if you have to work with the existing data structure, you can utilize the MySQL function FIND_IN_SET() along with a subquery to accomplish your goal.

Step-by-Step Guide

Fetch the Payroll Categories

Your first step would involve running a query to retrieve the payroll_cat_name from Table 2 that you will use for further operations.

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

Calculate the Sum of Amounts Using a Subquery

Instead of passing the string directly, you can construct a query that utilizes FIND_IN_SET() to efficiently sum the amounts from Table 1.

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

Final Code

The complete PHP code snippet combines everything discussed above:

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

Conclusion

By using the FIND_IN_SET() function in conjunction with a subquery, you can effectively retrieve and sum values across two tables based on foreign key relationships in MySQL. Though the initial database design may present challenges, understanding how to leverage SQL functions will empower you to efficiently manage and manipulate your data.

Remember that a better-designed database schema could simplify these operations, so consider revisiting your designs if you frequently encounter such situations.