我是wordpress的新手。我写了一个查询来获取以前和以后的帖子，但遇到了问题。（我检查

$sql = "
SELECT * FROM wp_posts WHERE post_date < ( SELECT post_date FROM wp_posts WHERE ID = {$id} ) LIMIT 1
UNION
SELECT * FROM wp_posts WHERE post_date > ( SELECT post_date FROM wp_posts WHERE ID =  {$id} ) LIMIT 1
";

$wpdb->query($sql);

$arrPosts = $wpdb->last_result;

但我只有一个职位在美元arrPosts。（我知道不止两个）。发生什么事了？

$arrPosts = $wpdb->get_results($sql);

get_next_post()
get_previous_post()