SQL queries to migrate all terms / posts from one taxonomy into another (WordPress)

WP Migrate From One Taxonomy to Another

-- This example is using a TARGET taxonomy of post_tag (WP native tags) and SOURCE of channel (custom taxonomy)
-- First, if desired, purge existing post relationships from target taxonomy
DELETE r FROM wp_term_relationships AS r 
    INNER JOIN wp_term_taxonomy AS t 
       ON r.term_taxonomy_id = t.term_taxonomy_id
    WHERE taxonomy = 'post_tag'

-- Then, if desired, purge existing terms from target taxonomy
DELETE FROM `wp_term_taxonomy` WHERE taxonomy = 'post_tag'

-- Finally, migrate all existing post relationships / terms from source to target
UPDATE wp_term_taxonomy SET taxonomy = 'post_tag' WHERE taxonomy = 'channel'