wp-admin/includes/post.php:1064Returns a list of previously defined keys.
string[]function get_meta_keys() { global $wpdb; $keys = $wpdb->get_col( "SELECT meta_key FROM $wpdb->postmeta GROUP BY meta_key ORDER BY meta_key" ); return $keys;}Introduced in 1.2.0. Unchanged from 6.7.7 through 7.1.0.
Signature, return type and hooks compared across 5 parsed releases.
src/wp-admin/includes/post.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.