The wp_term_taxonomy table is critical for organizing WordPress content. It stores information about categories, tags, and custom taxonomies, in addition to the information stored in wp_terms table. Most importantly, it stores the taxonomy for each term (e.g. "category" or "post_tag"), as well as which term is the parent (for hierrarchical taxonomies, like categories) and number of posts or pages assigned the term.
Columns
term_taxonomy_id: Unique identifier integer ID for each term in this table. It is also used in wp_term_relationships table to identify the term.
term_id: The term_id from wp_terms table, used to link the two tables together. It is often the same number as term_taxonomy_id, but does not have to be (so don't rely on it – they are two different IDs).
taxonomy: The name of the taxonomy, such as "category", "post_tag", or a custom taxonomy, such as "genre" (in a music site) or "destination" (in a travel site).
description: A brief description of the taxonomy.
parent: The ID of the parent term in the taxonomy hierarchy, if any. This allows for hierarchical taxonomies, such as categories, which have subcategories. For example, if a "Music" category has a subcategory "Rock", the parent value for "Rock" would be the term_id of "Music".
count: The number of objects (posts, pages, or custom post types) associated with the term. This value is cached by WordPress and updated whenever an object is associated or disassociated with a term. For example, if there are 10 posts assigned to the "Rock" category, the count value for that term in wp_term_taxonomy would be 10.
SQL Schema
CREATE TABLE `wp_term_taxonomy` (
`term_taxonomy_id` bigint(20) unsigned NOT NULL AUTO_INCREMENT,
`term_id` bigint(20) unsigned NOT NULL DEFAULT 0,
`taxonomy` varchar(32) COLLATE utf8mb4_unicode_ci NOT NULL DEFAULT '',
`description` longtext COLLATE utf8mb4_unicode_ci NOT NULL,
`parent` bigint(20) unsigned NOT NULL DEFAULT 0,
`count` bigint(20) NOT NULL DEFAULT 0,
PRIMARY KEY (`term_taxonomy_id`),
UNIQUE KEY `term_id_taxonomy` (`term_id`,`taxonomy`),
KEY `taxonomy` (`taxonomy`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;