I have two custom fields, and both have numeric values:
Custom Field 'tnid_01' exists for all posts.
Custom Field 'tnid_01old' only exists for some posts.
I am trying to replace the value of 'tnid_01' with the value of 'tnid_01old', but only if 'tnid_01old' exists.
This is what i have so far, but i get a mysql error:
Update wp_postmeta (post_id, meta_key, meta_value)( SELECT post_id, 'tnid_01', meta_value FROM wp_postmeta WHERE meta_key='tnid_01old' );