What are unused relationships?
WordPress stores the connections between posts and taxonomy terms (like categories or tags) in the wp_term_relationships table. Sometimes, when posts or taxonomies are deleted, their relationships remain in this table even though they no longer point to any valid post or term. These are called unused relationships.
How they affect your database?
Unused relationships clutter the wp_term_relationships table, creating unnecessary entries that increase database size and slightly slow down taxonomy queries. They can also cause inaccurate term counts and add extra load during backups and exports.
How to clean them?
1. Using Advanced Database Cleaner plugin
You can easily remove unused relationships using the General Cleanup module in Advanced Database Cleaner plugin.
The plugin automatically detects unused relationships and allows you to:
- Safely delete all unused relationships.
- Schedule automatic cleanups to prevent unnecessary buildup.
2. Using a raw SQL query
If you prefer a manual cleanup, you can run the following SQL command in phpMyAdmin for example:
DELETE FROM term_relationships WHERE term_taxonomy_id=1 AND object_id NOT IN (SELECT id FROM posts);
In multisite installations, execute this query for each subsite, replacing wp_ with the subsite’s prefix (for example, wp_2_, wp_3_, etc.).
Note:
While you can manually run these SQL commands to clean unused relationships, we strongly recommend using the Advanced Database Cleaner plugin.
It uses WordPress’s internal cleaning methods, automatically handles multisite installations, and ensures that all related data is safely removed while keeping your database consistent and stable.
