mysql - 如何获取在 MYSQL 8 中列值更改之前首次出现的选择行

Question

我有一个带有 Event_TimeStamp 和 FinalStateand 的 MYSQL8 表，它看起来像这样

+---------------------------+---------------+
|"Event_TimeStamp"          |"FinalState"   |
+---------------------------+---------------+
|"2020-03-09 04:57:45.729"  |"Available"    |
|"2020-03-09 05:14:59.659"  |"Available"    |
|"2020-03-09 05:27:56.341"  |"Available"    |
|"2020-03-09 05:41:01.554"  |"Available"    |
|"2020-03-09 05:58:07.803"  |"Available"    |
|"2020-03-09 06:06:09.745"  |"Available"    |
|"2020-03-09 06:18:07.663"  |"Available"    |
|"2020-03-09 06:26:24.273"  |"Available"    |
|"2020-03-09 09:29:53.165"  |"Offline"      |
|"2020-03-09 10:28:00.514"  |"Available"    |
|"2020-03-09 12:47:54.130"  |"Available"    |
|"2020-03-09 13:01:30.117"  |"Available"    |
|"2020-03-09 13:01:59.774"  |"Offline"      |
|"2020-03-09 13:19:15.772"  |"Available"    |
|"2020-03-09 14:19:51.521"  |"Available"    |
|"2020-03-09 14:50:16.872"  |"Offline"      |
+---------------------------+---------------+

我必须从上面提取行，这样它就会有第一个“可用”和“离线”的行，所以输出看起来像这样

+---------------------------+---------------+
|"Event_TimeStamp"          |"FinalState"   |
+---------------------------+---------------+
|"2020-03-09 04:57:45.729"  |"Available"    |
|"2020-03-09 09:29:53.165"  |"Offline"      |
|"2020-03-09 10:28:00.514"  |"Available"    |
|"2020-03-09 13:01:59.774"  |"Offline"      |
|"2020-03-09 13:19:15.772"  |"Available"    |
|"2020-03-09 14:50:16.872"  |"Offline"      |
+---------------------------+---------------+

我用 GROUP BY 尝试了几种方法，但我只得到每个 FinalState 的第一个条目，而不是其余的条目。

有没有办法通过查询来完成这项工作，还是我应该用 PHP 写出来？

Answer 1

您可以使用 lag() 和 lead() 来显示 final_state 与上一行或下一行不同的记录:

select
    event_timestamp,
    final_state
from (
    select 
        t.*, 
        lag(final_state) over(order by event_timestamp)  lag_final_state,
        lead(final_state) over(order by event_timestamp) lead_final_state
    from mytable t
) t
where final_state <> lag_final_state or final_state <> lead_final_state