WordPress WP\\u查询orderby 参数有很多选项，但没有一个选项像您所追求的那样具体。

我想你必须在通过WP_Query, 然后使用usort().

您的代码应该是这样的。

$args = array(
    \'post_type\' => \'z_day\',
    \'posts_per_page\' => -1,
    \'meta_query\' => array(
                      array( 
                         \'key\' => \'day_add_almanac\', 
                         \'value\' => \'yes\' 
                       )
                    ) 
    );

// Create object
$my_posts = new WP_Query( $args );

// Sort
usort( $my_posts->posts, function( $a, $b ) {

    // Convert "2018-01-28" to "0128"
    $c = str_replace(\'-\', \'\' ,substr($a->title , 5));
    $d = str_replace(\'-\', \'\' ,substr($b->title , 5));

    if( $c == $d ) {
        return 0;   
    }
    // Use < or > (or swap -1 and 1 ) for reversing order
    return ( $c > $d ) ? -1 : 1;  

});

// Loop
if( $my_posts->have_posts() ) {

    while( $my_posts->have_posts() ) {

        $my_posts->the_post();

        // Show posts
        the_title();

    }

}