Re: sql query question ? - Mailing list pgsql-sql

Trilok Kumar wrote:
> Hi All,
> 
> I have a table called 
> 
> vehicle_duty_cycle_summary 
> 
> 
> vehicle_master_id | starting_odometer |
> ending_odometer |         login_time         |       
> logout_time
> -------------------+-------------------+-----------------+----------------------------+----------------------------
> 
> 4 |          53379.00 |        53504.00 | 2006-12-19
> 16:19:16.584547 | 2006-12-20 07:12:57.716907

> 
> I would like to compute the following on this table.
> 
> Idle time of vehicel=(ending_odometer reading of the
> previous day -   
> starting_odometer reading of the present day) for
> every vehicle

I would think your naming may be confusing and may not be 
implemented(recorded?) very well.

I think Idle Time is a misleading name by your explanation - Idle time 
would be defined as (logout_time - previous login_time) which gives you 
the time the vehicle was sitting in the garage.

What you want may be better called unmetered_travel and would be the 
distance traveled between login_time and logout_time
This would simply be
select vehicle_master_id,
(ending_odometer - starting_odometer) as unmetered_travel
from vehicle_duty_cycle_summary;

Going by the naming you have used it would appear that you are recording 
the time spent in the garage (going by the data you have shown I would 
say this is a company car garage not a repair shop)

One record would appear to record the time the car is in the garage - 
login_time would be the time the employee returned the car and 
logout_time would be when the car next went out to someone.
I would think you want the opposite of that - the time and odometer 
reading when an employee takes the car and the time and odometer of when 
it is returned and the employee_id of who had it. This will give you who 
used the car at what time and what distances they travelled (which of 
course would be work related travel)

Going with those changes -

The distance traveled by an employee is easy to workout, if you wanted 
to workout the unmetered (non-work) distance traveled you could try 
something like (untested) -

select
v1.vehicle_master_id
, v1.starting_odometer - (select v2.ending_odometer  from vehicle_duty_cycle_summary v2
  where v2.vehicle_master_id = v1.vehicle_master_id  and v2.login_time < v1.logout_time
  order by v2.login_time desc limit 1)    as unmetered_travel

from vehicle_duty_cycle_summary v1

where v1.vehicle_master_id = 4;


I would calculate idle time as -

select
v1.vehicle_master_id
, v1.logout_time - (select v2.login_time  from vehicle_duty_cycle_summary v2
  where v2.vehicle_master_id = v1.vehicle_master_id  and v2.login_time < v1.logout_time
  order by v2.login_time desc limit 1)    as unmetered_travel

from vehicle_duty_cycle_summary v1

where v1.vehicle_master_id = 4;


If this isn't the way it should work you should be able to adapt the 
query to match your definition of idle time.


-- 

Shane Ambler
pgSQL (at) Sheeky (dot) Biz

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