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Accepted
Brian Leach
Asked: 2015-08-26 14:09:25 +0800 CST

找出差距和孤岛

  • 772

我有一个具有以下结构的数据库

+---------------------+------------+---------------+
| timestamp           | EngOilP_sd | CompOilLVL_sd |
+---------------------+------------+---------------+
| 2015-06-24 20:28:07 |          0 |             0 |
| 2015-06-24 20:30:20 |          1 |             0 |
| 2015-06-24 20:36:47 |          1 |             0 |
| 2015-06-24 20:41:11 |          1 |             0 |
| 2015-06-24 20:43:29 |          1 |             0 |
| 2015-06-24 20:45:42 |          0 |             0 |
| 2015-06-24 20:47:51 |          0 |             0 |
| 2015-06-24 20:49:59 |          0 |             1 |
| 2015-06-24 20:52:01 |          0 |             1 |
| 2015-06-24 20:54:17 |          0 |             0 |
+---------------------+------------+---------------+

我想生成如下报告：

sd             duration      start                    stop
EngOilP_sd     15min 22s     2015-06-24 20:30:20      2015-06-24 20:45:42
CompOilLVL_sd  4min 18s      2015-06-24 20:49:59      2015-06-24 20:54:17

我应该补充一点，停止记录是第一个值 = 0 的记录并不重要，它可能是最后一个值 = 1 的记录

我怎样才能轻松地创建一个性能良好的查询来提供我需要的信息？我在应用程序中使用 Python，因此我不需要 SQL 以这种确切的形式输出报告，只需让我了解信息的内容即可。

mysql gaps-and-islands

1 个回答

  1. Best Answer

    可能有比这更优雅的东西，但由于您正在做一种枢轴（从列转换为行，即元数据到数据），它永远不会很漂亮。假设像这样的表：

    create table t
( ts timestamp not null
, EngOilP_sd smallint not null
, CompOilLVL_sd smallint not null
) engine = innodb;

insert into t (ts, EngOilP_sd, CompOilLVL_sd)
values 
 ('2015-06-24 20:28:07',0 ,0 )
,('2015-06-24 20:30:20',1 ,0 )
,('2015-06-24 20:36:47',1 ,0 )
,('2015-06-24 20:41:11',1 ,0 )
,('2015-06-24 20:43:29',1 ,0 )
,('2015-06-24 20:45:42',0 ,0 )
,('2015-06-24 20:47:51',0 ,0 )
,('2015-06-24 20:49:59',0 ,1 )
,('2015-06-24 20:52:01',0 ,1 )
,('2015-06-24 20:54:17',0 ,0 );

    因为我们要多次引用“枢轴”，所以我们为它创建一个视图：

    create view t_pivot as 
    select 'EngOilP_sd' as sd, ts, EngOilP_sd as val from t 
    union all 
    select 'CompOilLVL_sd', ts, CompOilLVL_sd from t;

    开始时间（以@Pauls注释为定义）是各属性为1的最早时间：

    select sd, min(case val when 1 then ts end) as start
from t_pivot     
group by sd

    停止时间是每个属性为 0 之后的最早时间：

    select x.sd, x.start, min(case y.val when 0 then y.ts end) as stop
from (
    select sd, min(case val when 1 then ts end) as start
    from t_pivot     
    group by sd 
) as x 
join t_pivot as y
    on x.sd = y.sd
   and y.ts > x.start 
group by x.sd, x.start

    添加另一层嵌套可以方便地确定持续时间：

    select sd, timediff(stop, start) as duration, start, stop 
from ( 
    select x.sd, x.start, min(case y.val when 0 then y.ts end) as stop
    from (
        select sd, min(case val when 1 then ts end) as start
        from t_pivot     
        group by sd 
    ) as x 
    join t_pivot as y
        on x.sd = y.sd
       and y.ts > x.start 
    group by x.sd, x.start 
) as z 
order by sd desc;

+---------------+----------+---------------------+---------------------+
| sd            | duration | start               | stop                |
+---------------+----------+---------------------+---------------------+
| EngOilP_sd    | 00:15:22 | 2015-06-24 20:30:20 | 2015-06-24 20:45:42 |
| CompOilLVL_sd | 00:04:18 | 2015-06-24 20:49:59 | 2015-06-24 20:54:17 |
+---------------+----------+---------------------+---------------------+
2 rows in set (0.00 sec)
    • 3

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