Modify the search "WHERE" statement in WordPress

search_where_filter

add_filter('posts_search', 'what_the_search', $priority = 10, $accepted_args = 2);
function what_the_search( $search, $query ){
  if ( $query->is_search ) {
    $towrite = PHP_EOL . '$search: ' . print_r( $search, TRUE );
    // $search looks like:
    // AND (((wp_posts.post_title LIKE '%walking%') OR (wp_posts.post_content LIKE '%walking%')))  AND (wp_posts.post_password = '')
    $fp = fopen('what_the_search.txt', 'a');
    fwrite($fp, $towrite);
    fclose($fp);
  }
}