数据库查询：GROUPing提取第一行和最后一行

时间：2017-04-20 20:05:47

标签： postgresql group-by window-functions postgresql-9.4 gaps-and-islands

我有以下“开始”查询：

select fecha as date,velocidad as speed, velocidad>100 as overspeed 
from reports.avl_historico_354898046636089 
where fecha between '2017-04-19 00:00:00-03' and '2017-04-20 00:00:00-03'
and velocidad>2 and ignicion=1
order by fecha;

产生以下输出：

date                  speed overspeed

2017-04-19 11:35:41+00,16,f
2017-04-19 11:37:01+00,24,f
2017-04-19 11:37:41+00,72,f
2017-04-19 11:38:21+00,82,f
2017-04-19 11:39:01+00,13,f
2017-04-19 11:39:41+00,68,f
2017-04-19 11:40:21+00,23,f
2017-04-19 11:41:01+00,57,f
2017-04-19 11:41:41+00,97,f
2017-04-19 11:42:21+00,96,f
2017-04-19 11:43:01+00,102,t
2017-04-19 11:43:41+00,104,t
2017-04-19 11:44:21+00,106,t
2017-04-19 11:45:01+00,109,t
2017-04-19 11:45:41+00,109,t
2017-04-19 11:46:21+00,114,t
2017-04-19 11:47:01+00,56,f
2017-04-19 11:47:28+00,54,f
2017-04-19 11:47:41+00,54,f
2017-04-19 11:48:21+00,54,f
2017-04-19 11:49:01+00,102,t
2017-04-19 11:49:07+00,104,t
2017-04-19 11:54:21+00,114,t
2017-04-19 11:55:01+00,118,t
2017-04-19 11:55:41+00,115,t
2017-04-19 11:56:21+00,111,t
2017-04-19 11:57:01+00,85,f
2017-04-19 11:57:41+00,45,f
2017-04-19 11:58:21+00,29,f
2017-04-19 12:00:35+00,4,f
2017-04-19 12:00:36+00,4,f
...

我一直在尝试使用LAG/LEAD来获取overspeed列为TRUE的每组行的第一个/最后一个日期，但我还没有能够达到预期的效果，可能是这样的：

start                     stop
2017-04-19 11:43:01+00    2017-04-19 11:46:21+00
2017-04-19 11:49:01+00    2017-04-19 11:56:21+00

任何有关如何获得此类输出的想法都将受到赞赏。

原始表DDL：

CREATE TABLE avl_historico_354898046636089 (
    fecha timestamp with time zone NOT NULL,
    latitud double precision DEFAULT 0 NOT NULL,
    longitud double precision DEFAULT 0 NOT NULL,
    altitud double precision DEFAULT 0 NOT NULL,
    velocidad double precision DEFAULT 0 NOT NULL,
    cog double precision DEFAULT 0 NOT NULL,
    nsat integer DEFAULT 0 NOT NULL,
    tipo character(1),
    utc_hora time without time zone,
    fix_fecha date,
    imei bigint NOT NULL,
    registro timestamp with time zone,
    input1 integer DEFAULT 0,
    input2 integer DEFAULT 0,
    input3 integer DEFAULT 0,
    input4 integer DEFAULT 0,
    hdop double precision,
    adc double precision DEFAULT (-99),
    ignicion integer DEFAULT 1,
    adc2 double precision,
    power integer,
    driverid integer,
    ibutton2 integer,
    ibutton3 integer,
    ibutton4 integer,
    trailerid integer,
    adc3 double precision,
    adc4 double precision,
    horometro bigint,
    odometro bigint,
    panico integer DEFAULT 0,
    bateria double precision,
    bateriaint double precision
);

3 个答案:

答案 0 :(得分：1)

SELECT grp, min(date) AS start, max(date) AS stop
FROM (

    SELECT date, speed, count(is_reset) OVER () AS grp
    FROM (

        SELECT
          date,
          speed,
          CASE
            WHEN overspeed <> lag(overspeed) OVER (ORDER BY date) THEN 1
          END AS is_reset
        FROM (

            select fecha as date,velocidad as speed, velocidad>100 as overspeed 
            from reports.avl_historico_354898046636089 
            where fecha between '2017-04-19 00:00:00-03' and '2017-04-20 00:00:00-03'
            and velocidad>2 and ignicion=1

        ) AS t

    ) AS t2

) AS t3
GROUP BY grp;

答案 1 :(得分：1)

这是一个GROUPING和WINDOW示例。

注意我编辑了一些结果只是为了缩小它。

create table test (fecha timestamp, velocidad int, overspeed  bool);
insert into test values
('2017-04-19 20:18:17+00',  77,  FALSE),
('2017-04-19 20:18:57+00',  96,  FALSE),
('2017-04-19 20:19:37+00',  108, TRUE),
('2017-04-19 20:20:17+00',  111, TRUE),
('2017-04-19 20:20:57+00',  114, TRUE),
('2017-04-19 20:21:37+00',  112, TRUE),
('2017-04-19 20:22:17+00',  108, FALSE),
('2017-04-19 20:22:57+00',  107, FALSE),
('2017-04-19 20:23:37+00', 113, FALSE),
('2017-04-19 20:24:17+00', 116, TRUE),
('2017-04-19 20:24:57+00',  111, TRUE),
('2017-04-19 20:25:37+00',  113, TRUE),
('2017-04-19 20:26:17+00',  115, FALSE),
('2017-04-19 20:26:28+00',  115, FALSE),
('2017-04-19 20:26:57+00',  115, TRUE),
('2017-04-19 20:27:37+00',  115, TRUE),
('2017-04-19 20:27:58+00',  60,  FALSE);

with ResetPoint as
(
    select fecha, velocidad, overspeed,
           case when lag(overspeed) over (order by fecha) = overspeed then null else 1 end as reset
    from test
)
    --= Set a group each time overspeed changes
    , SetGroup as
    (
        select fecha, velocidad, overspeed, 
               count(reset) over (order by fecha) as grp
        from ResetPoint
    )
    select *
    from SetGroup;

fecha               | velocidad | overspeed | grp
:------------------ | --------: | :-------- | --:
2017-04-19 20:18:17 |        77 | f         |   1
2017-04-19 20:18:57 |        96 | f         |   1
2017-04-19 20:19:37 |       108 | t         |   2
2017-04-19 20:20:17 |       111 | t         |   2
2017-04-19 20:20:57 |       114 | t         |   2
2017-04-19 20:21:37 |       112 | t         |   2
2017-04-19 20:22:17 |       108 | f         |   3
2017-04-19 20:22:57 |       107 | f         |   3
2017-04-19 20:23:37 |       113 | f         |   3
2017-04-19 20:24:17 |       116 | t         |   4
2017-04-19 20:24:57 |       111 | t         |   4
2017-04-19 20:25:37 |       113 | t         |   4
2017-04-19 20:26:17 |       115 | f         |   5
2017-04-19 20:26:28 |       115 | f         |   5
2017-04-19 20:26:57 |       115 | t         |   6
2017-04-19 20:27:37 |       115 | t         |   6
2017-04-19 20:27:58 |        60 | f         |   7

--= Set a reset point each time overspeed changes
--
with ResetPoint as
(
    select fecha, velocidad, overspeed,
           case when lag(overspeed) over (order by fecha) = overspeed then null else 1 end as reset
    from test
)
    --= Set a group each time overspeed changes
    , SetGroup as
    (
        select fecha, velocidad, overspeed, 
               count(reset) over (order by fecha) as grp
        from ResetPoint
    )
    --= Retruns MIN and MAX date of each group
    select grp, min(fecha) as Start, max(fecha) as End
    from SetGroup
    group by grp;

grp | start               | end                
--: | :------------------ | :------------------
  4 | 2017-04-19 20:24:17 | 2017-04-19 20:25:37
  1 | 2017-04-19 20:18:17 | 2017-04-19 20:18:57
  5 | 2017-04-19 20:26:17 | 2017-04-19 20:26:28
  3 | 2017-04-19 20:22:17 | 2017-04-19 20:23:37
  6 | 2017-04-19 20:26:57 | 2017-04-19 20:27:37
  2 | 2017-04-19 20:19:37 | 2017-04-19 20:21:37
  7 | 2017-04-19 20:27:58 | 2017-04-19 20:27:58

dbfiddle here

答案 2 :(得分：1)

这可以更简单。减去两个row_number()来电：

SELECT min(date) AS start
     , max(date) AS stop
FROM  (
   SELECT date, overspeed
        , row_number() OVER (ORDER BY date)
        - row_number() OVER (PARTITION BY overspeed ORDER BY date) AS grp
   FROM tbl  -- result of your starting query
   ) sub
WHERE  overspeed
GROUP  BY grp
ORDER  BY grp;

第1个生成所有的运行编号，第2个按overspeed分区。当您从第一个组中减去第二个时，每个组最终都有相同的组号，每个分区不同。

然后在外部查询中使用overspeed过滤那些并使用min＆amp;每组最大值。瞧。

详细说明：

除此之外：时间戳不是日期。这是一个令人困惑的专栏名称。

集成子查询

发表评论。将tbl替换为原始查询作为子查询，如下所示：

SELECT min(date) AS start
     , max(date) AS stop
FROM  (
   SELECT date, overspeed
        , row_number() OVER (ORDER BY date)
        - row_number() OVER (PARTITION BY overspeed ORDER BY date) AS grp
   FROM (
      SELECT fecha AS date, velocidad AS speed, velocidad > 100 AS overspeed 
      FROM   reports.avl_historico_354898046636089 
      WHERE  fecha >= '2017-04-19 00:00:00-03'  -- typically, you include the lower
      AND    fecha <  '2017-04-20 00:00:00-03'  -- and exclude the upper bound
      AND    velocidad > 2
      AND    ignicion = 1
      -- drop the now useless inner ORDER BY
      ) sub1
   ) sub2
WHERE  overspeed
GROUP  BY grp
ORDER  BY grp;

然后你可以简化一些：

SELECT min(fecha) AS start
     , max(fecha) AS stop
FROM  (
   SELECT fecha, velocidad > 100 AS overspeed 
        , row_number() OVER (ORDER BY fecha)
        - row_number() OVER (PARTITION BY velocidad > 100 ORDER BY fecha) AS grp
   FROM   reports.avl_historico_354898046636089 
   WHERE  fecha >= '2017-04-19 00:00:00-03'
   AND    fecha <  '2017-04-20 00:00:00-03'
   AND    velocidad > 2
   AND    ignicion = 1
   ) sub
WHERE  overspeed
GROUP  BY grp
ORDER  BY grp;
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