如何为所有拥有此meta的帖子更新自定义meta（likes）？

If you want to update every post that has this meta:

Something like this (untested):

$args = array( \'fields\'          => \'ids\', 
               \'posts_per_page\'  => -1, 
               \'post_type\'       => \'posts\', 
               \'meta_key\'        => \'likes\' 
               );
$all_ids = new WP_Query( $args );

foreach( $all_ids as $ai ) {

   update_post_meta( $ai->post->ID, \'likes\', 1 );
}
wp_reset_postdata();