Turning Wordpress Categories Into Tags


Category: Code
Tags: MySQL  SQL    WordPress   automation insert into select

I recently updated this Wordpress install from 2.2.something to 2.5 and noticed that it now supports tags instead of just categories. I had been using categories as tags, but I’d rather built-in tags than fake it anymore. I didn’t want to manually retag a couple hundred posts with ~200 tags, so I wrote some SQL to do it for me. If you’re in the same boat

Warning: This could break and completely mess up your categories and tags. I’m only promising this worked for me on my install for now (who knows, maybe I updated things wrong and huge problems will occur a month from now). Use caution. I take no responsibility.

# create tags for every category insert into wp_term_taxonomy (term_id, taxonomy) select term_id, “post_tag” from wp_term_taxonomy where taxonomy = ‘category’;

# copy category-post relationships to tag-post relationships insert into wp_term_relationships (object_id, term_taxonomy_id) select object_id, (select i.term_taxonomy_id from wp_term_taxonomy i where taxonomy = ‘post_tag’ and i.term_id = wp_term_taxonomy.term_id) from wp_term_relationships join wp_term_taxonomy on wp_term_relationships.term_taxonomy_id = wp_term_taxonomy.term_taxonomy_id where taxonomy = ‘category’;

# update tag count cache update wp_term_taxonomy set count = (select count(*) from wp_term_relationships where wp_term_relationships.term_taxonomy_id = wp_term_taxonomy.term_taxonomy_id);

# remove all categories and category-post relationships delete from wp_term_taxonomy where taxonomy = ‘category’; delete from wp_term_relationships where term_taxonomy_id not in (select term_taxonomy_id from wp_term_taxonomy);

The INSERT INTO \... SELECT was a fun little query to write with its subselect. After running this, I just had to create and apply categories to my posts (I’m going with Biz, Code, Games, and Life for now) and update my templates.