Split table data based on time gaps-CodePudding

Let's say we have a time-series dataset of entities metadata imported into postgres table Stats:

CREATE EXTENSION IF NOT EXISTS POSTGIS;
DROP TABLE IF EXISTS "Stats";
CREATE TABLE IF NOT EXISTS "Stats"
(
    "time" BIGINT,
    "id" BIGINT,
    "position" GEOGRAPHY(PointZ, 4326)
);

And here is the samples of table:

SELECT 
    "id",
    "time"
FROM
    "Stats"
ORDER BY 
    "id", "time" ASC

id|time|
-- ---- 
 1|   3|
 1|   4|
 1|   6|
 1|   7|
 2|   2|
 2|   6|
 3|  14|
 4|   2|
 4|   9|
 4|  10|
 4|  11|
 5|  32|
 6|  15|
 7|  16|

The business requirement is to assign route-id to entities in this table, so when the time for each entity jump over 1 second it means the new flight or route for that entity. the final result would like this for previous samples:

id|time|route_id|
-- ---- -------- 
 1|   3|       1|
 1|   4|       1|
 1|   6|       2|
 1|   7|       2|
 2|   2|       1|
 2|   6|       2|
 3|  14|       1|
 4|   2|       1|
 4|   9|       2|
 4|  10|       2|
 4|  11|       2|
 5|  32|       1|
 6|  15|       1|
 7|  16|       1|

And this would be the new summary table of the routes:

id|start_time|end_time|route_id|
-- ---------- -------- -------- 
 1|         3|       4|       1|
 1|         6|       7|       2|
 2|         2|       2|       1|
 2|         6|       6|       2|
 3|        14|      14|       1|
 4|         2|       2|       1|
 4|         9|      11|       2|
 5|        32|      32|       1|
 6|        15|      15|       1|
 7|        16|      16|       1|

So how this complex query should be constructed?

CodePudding user response：

with data as (
    select *, row_number() over (partition by id order by "time") rn from Stats
)
select id,
    min("time") as start_time, max("time") as end_time,
    row_number() over (partition by id order by "time" - rn) as route_id
from data
group by id, "time" - rn
order by id, "time" - rn

https://dbfiddle.uk/?rdbms=postgres_9.5&fiddle=c272bc57786487b0b664648139530ae4

CodePudding user response：

Assuming you have table stats in hand, the following query will create a table by assigning route_id:

Query to assign route_id using recursive-cte:

CREATE TABLE tbl_route AS 
with recursive cte AS 
(
  SELECT id,  prev_time, time, rn, rn AS ref_rn, rn AS route_id 
  FROM 
  (    
    SELECT 
      *,
      lag(time) OVER(partition BY id ORDER BY time) AS prev_time,
      row_number() OVER(partition BY id ORDER BY time) AS rn 
    FROM stats
  ) AS rnt
  WHERE rn=1

  UNION

  SELECT rnt2.id, rnt2.prev_time, rnt2.time, rnt2.rn, cte.rn AS ref_rn,
    CASE 
      WHEN abs(rnt2.time-rnt2.prev_time)<=1 THEN cte.route_id
      ELSE cte.route_id 1
    END AS route_id
  FROM cte
  INNER JOIN
  (
   SELECT 
     *,
     lag(time) OVER(partition BY id ORDER BY time) AS prev_time,
     row_number() OVER(partition BY id ORDER BY time) AS rn 
   FROM stats
  ) AS rnt2
   ON cte.id=rnt2.id AND cte.rn 1 = rnt2.rn
)

SELECT id, time, route_id FROM cte;

Query to check if route_id assigned was correct:

select id, time, route_id 
from tbl_route 
order by id, time

Query to create new summary table:

select id, min(time) as start_time, max(time) as end_time, route_id
from tbl_route
group by id, route_id
order by id, route_id, start_time, end_time

Recursive-CTE Query breakdown:

Since recursive cte has been used, the query may look messy. However, I tried to break it down as follows:

There are 2 main queries getting appended using UNION, First one will assign route_id for start of each id, Second will do it for rest of the rows for each id
rnt and rnt2 has been created because we need ROW_NUMBER and LAG values to achieve this
We joined cte and rnt2 recursively to assign route_id by checking the difference in the time

DEMO