WordPress 功能增强代码：添加历史上的今天

WordPress 可以通过显示相关文章来增加页面浏览量，另一种方法就是显示历史上的今天，可以看到更早之前同一天更新过哪些文章，原理就是通过查询数据库里日期和今天 一样的文章，并用 add_filter 函数把 HTML 代码更新到文章内容变量 the_content 里，荒岛本次带来 WordPress 添加历史上的今天教程，只要将下面的代码添加到主题的「functions.php」文件即可。

// 荒岛一座藏有宝藏的小岛
function hd_today(){
    global $wpdb;
    $today_post = '';
    $result = '';
    $post_year = get_the_time('Y');
    $post_month = get_the_time('m');
    $post_day = get_the_time('j');
    $sql = "select ID, year(post_date_gmt) as today_year, post_title, comment_count FROM 
            $wpdb->posts WHERE post_password = '' AND post_type = 'post' AND post_status = 'publish'
            AND year(post_date_gmt)!='$post_year' AND month(post_date_gmt)='$post_month' AND day(post_date_gmt)='$post_day'
            order by post_date_gmt DESC limit 7";
    $histtory_post = $wpdb->get_results($sql);
    if( $histtory_post ){
        foreach( $histtory_post as $post ){
            $today_year = $post->today_year;
            $today_post_title = $post->post_title;
            $today_permalink = get_permalink( $post->ID );
            $today_post .= '<li><a href="'.$today_permalink.'" target="_blank"><span>'.$today_year.'</span>'.$today_post_title.'</a></li>';
        }
    }
    if ( $today_post ){
        $result = '<div class="begin-today"><fieldset><legend><h5>'. sprintf(__( '历史上的今天', 'begin' )) .'</h5></legend><div class="today-date"><div class="today-m">'.get_the_date( 'F' ).'</div><div class="today-d">'.get_the_date( 'j' ).'</div></div><ul>'.$today_post.'</ul></fieldset></div>';
    }else{
        $result = '<div class="begin-today"><fieldset><legend><h5>'. sprintf(__( '历史上的今天', 'begin' )) .'</h5></legend><div class="today-date"><div class="today-m">'.get_the_date( 'F' ).'</div><div class="today-d">'.get_the_date( 'j' ).'</div></div><div><span class="nfhd">'.get_the_time('Y').'</span>&nbsp;&nbsp;荒岛宝藏 即将发布 敬请期待...</div></fieldset></div>';
    }
    return $result;
}