查询的记录，其中存在具有最大（日）

Question

我试图创建一个查询发现，具有小于20分钟老

这是一个心跳的日期至少一个记录线程表看起来像这样：

+--------------+-----------+---------------------+---------------------+ 
| heartbeat_id | server_id | thread    | last_checkin  | 
+--------------+-----------+---------------------+---------------------+ 
|   3 |  133 | EscalationMonitor | 2016-03-16 23:46:07 | 
|   7 |  133 | EmailMonitor  | 2016-03-16 23:47:31 | 
|   11 |  133 | TableMonitor  | 2016-03-16 23:42:49 | 
|   15 |  133 | NotificationMonitor | 2016-03-16 23:46:30 | 
|   19 |  127 | EmailMonitor  | 2016-03-16 23:47:21 | 
|   23 |  127 | TableMonitor  | 2016-03-16 23:46:11 | 
|   27 |  127 | EscalationMonitor | 2016-03-16 23:47:58 | 
|   31 |  127 | NotificationMonitor | 2016-03-16 23:41:10 | 
|   35 |  123 | EmailMonitor  | 2016-03-16 23:47:59 | 
|   39 |  123 | TableMonitor  | 2016-03-16 23:43:10 | 
|   43 |  123 | EscalationMonitor | 2016-03-16 23:46:26 | 
|   47 |  123 | NotificationMonitor | 2016-03-16 23:46:47 | 
+--------------+-----------+---------------------+---------------------+ 

这是我在哪里，但这种搜索至少一个记录超过20分钟岁。

SELECT * FROM heartbeat h WHERE exists 
(
    select * from heartbeat h2 
    where last_checkin < date_add(now(), INTERVAL - 20 MINUTE) 
) 
group by thread 

Answer 1

如果你想有至少1签了20多分钟前线程，你可以把这个条件在where子句中，并使用不同的删除重复：

select distinct thread from heartbeat 
where last_checkin > date_sub(now(), INTERVAL 20 MINUTE) 

要检索的所有主题有未签到不到20分钟的时候：

select thread from heartbeat 
group by thread 
having count(case when last_checkin > date_sub(now(), INTERVAL 20 MINUTE) then 1 end) = 0 

如果你有一个threads表，那么你可以利用not exists

select * from threads t where not exists (
    select 1 from heartbeat h 
    where t.thread = h.thread 
    and h.last_checkin > date_sub(now(), INTERVAL 20 MINUTE) 
) 

Answer 2

从INTERVAL - 20 MINUTE