Calculate Average time spend based on a change in location zone - sql

Question

I have a table similar to
create table LOCHIST
(
RES_ID VARCHAR(10) NOT NULL,
LOC_DATE TIMESTAMP NOT NULL,
LOC_ZONE VARCHAR(10)
)
with values such as
insert into LOCHIST values(0911,2015-09-23 12:27:00.000000,SYLVSYLGA);
insert into LOCHIST values(5468,2013-02-15 13:13:24.000000,30726);
insert into LOCHIST values(23894,2013-02-15 13:12:13.000000,BECTFOUNC);
insert into LOCHIST values(24119,2013-02-15 13:12:09.000000,30363);
insert into LOCHIST values(7101,2013-02-15 13:11:37.000000,37711);
insert into LOCHIST values(26083,2013-02-15 13:11:36.000000,SHAWANDAL);
insert into LOCHIST values(24978,2013-02-15 13:11:36.000000,38132);
insert into LOCHIST values(26696,2013-02-15 13:11:27.000000,29583);
insert into LOCHIST values(5468,2013-02-15 13:11:00.000000,37760);
insert into LOCHIST values(5552,2013-02-15 13:10:55.000000,30090);
insert into LOCHIST values(24932,2013-02-15 13:10:48.000000,JBTTLITGA);
insert into LOCHIST values(23894,2013-02-15 13:10:42.000000,47263);
insert into LOCHIST values(26803,2013-02-15 13:10:25.000000,32534);
insert into LOCHIST values(24434,2013-02-15 13:10:03.000000,PLANSUFVA);
insert into LOCHIST values(26696,2013-02-15 13:10:00.000000,GEORALBGA);
insert into LOCHIST values(5468,2013-02-15 13:09:54.000000,19507);
insert into LOCHIST values(23894,2013-02-15 13:09:48.000000,37725);
This table literally goes on for millions of records.
Each RES_ID represents the ID of a trailer who pings their location to a LOC_ZONE which is then stored at the time in LOC_DATE.
What I am trying to find, is the average amount of time spent for all trailers in a specific location zone. For example, if trailer x spent 4 hours in in loc zone PLANSUFVA, and trailer y spent 6 hours in loc zone PLANSUFVA I would want to return
Loc Zone Avg Time
PLANSUFVA 5
Is there anyway to do this without cursors?
I really appreciate your help.

Answer 1

This needs SQL 2012:
with data
as (
select *, (case when LOC_ZONE != PREVIOUS_LOC_ZONE or PREVIOUS_LOC_ZONE is null then ROW_ID else null end) as STAY_START, (case when LOC_ZONE != NEXT_LOC_ZONE or NEXT_LOC_ZONE is null then ROW_ID else null end) as STAY_END
from (
select RES_ID, LOC_ZONE, LOC_DATE, lead(LOC_DATE, 1) over (partition by RES_ID, LOC_ZONE order by LOC_DATE) as NEXT_LOC_DATE, lag(LOC_ZONE, 1) over (partition by RES_ID order by LOC_DATE) as PREVIOUS_LOC_ZONE, lead(LOC_ZONE, 1) over (partition by RES_ID order by LOC_DATE) as NEXT_LOC_ZONE, ROW_NUMBER() over (order by RES_ID, LOC_ZONE, LOC_DATE) as ROW_ID
from LOCHIST
) t
), stays as (
select * from (
select RES_ID, LOC_ZONE, STAY_START, lead(STAY_END, 1) over (order by ROWID) as STAY_END
from (
select RES_ID, LOC_ZONE, STAY_START, STAY_END, ROW_NUMBER() over (order by RES_ID, LOC_ZONE, STAY_START desc) as ROWID
from data
where STAY_START is not null or STAY_END is not null
) t
) t
where STAY_START is not null and STAY_END is not null
)
select s.LOC_ZONE, avg(datediff(second, LOC_DATE, NEXT_LOC_DATE)) / 60 / 60 as AVG_IN_HOURS
from data d
inner join stays s on d.RES_ID = s.RES_ID and d.LOC_ZONE = s.LOC_ZONE and d.ROW_ID >= s.STAY_START and d.ROW_ID < s.STAY_END
group by s.LOC_ZONE

Answer 2

To solve this problem, you need the amount of time spent at each location.
One way to do this is with a correlated subquery. You need to group adjacent values. The idea is to find the next value in the sequence:
select resid, min(loc_zone) as loc_zone, min(loc_date) as StartTime,
max(loc_date) as EndTime,
nextdate as NextStartTime
from (select lh.*,
(select min(loc_date) from lochist lh2
where lh2.res_id = lh.res_id and lh2.loc_zone <> lh.loc_zone and
lh2.loc_date > lh.loc_date
) as nextdate
from lochist lh
) lh
group by lh.res_id, nextdate
With this data, you can then get the average that you want.
I am not clear if the time should be based on EndTime - StartTime (last recorded time at the location minus the first recorded time) or NextStartTime - startTime (first time at next location minus first time at this location).
Also, this returns NULL for the last location for each res_id. You don't say what to do about the last in the sequence.
If you build an index on res_id, loc_date, loc_zone, it might run faster.
If you had Oracle or SQL Server 2012, the right query is:
select lh.*,
lead(loc_date) over (partition by res_id order by loc_date) as nextdate
from (select lh.*,
lag(loc_zone) over (partition by res_id order by loc_date) as prevzone
from lochist lh
) lh
where prevzone is null or prevzone <> loc_zone
Now you have one row per stay and nextdate is the date at the next zone.

Answer 3

This should get you each zone ordered by the average number of minutes spent in it. The CROSS APPLY returns the next ping in a different zone.
SELECT
loc.LOC_ZONE
,AVG(DATEDIFF(mi,loc.LOC_DATE,nextPing.LOC_DATE)) AS avgMinutes
FROM LOCHIST loc
CROSS APPLY(
SELECT TOP 1 loc2.LOC_DATE
FROM LOCHIST loc2
WHERE loc2.RES_ID = loc.RES_ID
AND loc2.LOC_DATE > loc.LOC_DATE
AND loc2.LOC_ZONE <> loc.LOC_ZONE
ORDER BY loc2.LOC_DATE ASC
) AS nextPing
GROUP BY loc.LOC_ZONE
ORDER BY avgMinutes DESC

Answer 4

My variation of the solution:
select LOC_ZONE, avg(TOTAL_TIME) AVG_TIME from (
select RES_ID, LOC_ZONE, sum(TIME_SPENT) TOTAL_TIME
from (
select RES_ID, LOC_ZONE, datediff(mi, lag(LOC_DATE, 1) over (
partition by RES_ID order by LOC_DATE), LOC_DATE) TIME_SPENT
from LOCHIST
) t
where TIME_SPENT is not null
group by RES_ID, LOC_ZONE) f
group by LOC_ZONE
This accounts for multiple stays at the same location. The choice between lag or lead depends if a stay should start or end with the ping (ie, if one trailer sends a ping from A and then x hours later from B, does that count for A or B).

Answer 5

To do this without using either a cursor or a correlated subquery, try:
with rl as
(select l.*, rank() over (partition by res_id order by loc_date) rn
from lochist l),
fdr as
(select rc.*, coalesce(rn.loc_date, getdate()) next_date
from rl rc
left join rl rn on rc.res_id = rn.res_id and rc.rn + 1 = rn.rn)
select loc_zone, avg(datediff(second, loc_date, next_date))/3600 avg_time
from fdr
group by loc_zone
SQLFiddle here.
(Because of the way that SQLServer calculates time differences, it's probably better to calculate the average time in seconds and then divide by 60*60. With the exception of the getdate() and datediff clauses - which can be replaced by sysdate and next_date - loc_date - this should work in both SQLServer 2005 onwards and Oracle 10g onwards.)