php - MYSQL 排序依据和分组依据

Question

我目前有这个

SELECT type, extra_id, COUNT(*) AS count, id 
FROM `notifications` 
WHERE `receiver_id` = '".$this->user_id."' 
    AND `read` = '0' 
GROUP BY type, extra_id 
ORDER BY `id` DESC

但这仅按数据库中第一个找到的结果进行排序，因为这是我 SELECT id 时所采取的结果。我该如何做到这一点，以便从 notifications 中获取最后找到的 ID 以在 SELECT id 中使用？

Answer 1

只需选择MAX(id)而不是id:

SELECT type, extra_id, COUNT(*) AS count, MAX(id) AS max_id
FROM `notifications` 
WHERE `receiver_id` = '".$this->user_id."' 
    AND `read` = '0' 
GROUP BY type, extra_id 
ORDER BY max_id DESC