For some reason you sometimes need to add a custom field to all your existing posts. You can do it manually, but if you have lots of posts, the process will take a while. Here is a simple way to add a custom field to all posts quickly and easily.
Simply run the following SQL query on your WordPress database, using the command line client or PhpMyAdmin. This will automatically ad a custom field named MyCustomField to all your existing posts.
Don’t forget to backup your database before using this query.
INSERT INTO wp_postmeta (post_id, meta_key, meta_value) SELECT ID AS post_id, 'MyCustomField' AS meta_key 'myvalue AS meta_value FROM wp_posts WHERE ID NOT IN (SELECT post_id FROM wp_postmeta WHERE meta_key = 'MyCustomField') `` AND post_type = 'post';
Thanks to Abhishek for the tip!