WordPress is a powerful platform that comes with its own set of conventions, including the use of custom post types, taxonomies, and post meta for organizing and storing data. However, there are situations where you might find the need to create custom tables for your plugin. In this how-to article, we’ll guide you through the process, addressing concerns raised in a discussion about recreating WordPress tables.

Understanding the Situation

In the discussion, the user expresses confusion about the absence of FOREIGN KEY in WordPress tables, particularly in the context of creating custom tables for a plugin. The user wants to link tables similar to how term_id in wp_term_taxonomy would link to wp_terms using FOREIGN KEY. However, WordPress primarily uses UNIQUE KEY and KEY in its SQL syntax.

Step 1: Why Foreign Keys Aren’t Essential

WordPress doesn’t rely on FOREIGN KEY constraints for linking tables. The absence of foreign keys doesn’t hinder the platform’s ability to manage relationships between different types of data. Instead, it uses conventions and PHP logic to handle these connections at the application level.

Step 2: Recreating Tables for Your Plugin

The user in the discussion wants to recreate terms, taxonomy, and relationship tables from WordPress in their plugin. However, it’s cautioned that this approach may introduce compatibility issues and increased development effort. WordPress recommends using custom post types, custom taxonomies, and post meta for handling additional data associated with objects.

Step 3: Considerations for Custom Tables

Despite the warnings, if you decide to proceed with custom tables, keep a few considerations in mind:

Step 4: Understanding WordPress Query Mechanism

WordPress fetches data using SQL queries and JOIN statements constructed in PHP. For instance, when querying post meta, it selects rows with matching IDs in a follow-up query or a JOIN. WordPress classes like WP_Query and WP_Term_Query help in constructing these queries.

Step 5: Handling Relationships Without Foreign Keys

In WordPress, relationships between tables are managed at the application level. There’s no automatic database-level linking. When querying, WordPress might use JOIN to select related data, but this is done in PHP, not at the database level.


While the user in the discussion seeks to understand how MySQL associates IDs without explicitly using FOREIGN KEY, it’s essential to grasp that WordPress relies on conventions and PHP logic rather than strict database constraints. In your plugin development, consider alternatives like custom post types and taxonomies, and only resort to custom tables if absolutely necessary, understanding the potential challenges and trade-offs.

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