# [postgis-users] SQL moving window averages/statistics

Paragon Corporation lr at pcorp.us
Wed Sep 23 22:34:00 PDT 2009

```Kai,

Still not quite sure what you are doing here, but if you are using
PostgreSQL 8.4 you can use the
New windowing functions lead(), lag() will give you forward and backward
values.  I put in 1 and 1 for example, but if you wanted to count back say 5
records from your current you would replace with 5

http://www.postgresql.org/docs/8.4/interactive/functions-window.html

So something like

SELECT date, tmax As curr_tmax, lag(tmax,1) OVER(ORDER BY date) As
previous_day_tmax, lead(tmax,+1) OVER(ORDER BY date) As next_day_tmax
FROM daily_climate;

Leo

-----Original Message-----
From: postgis-users-bounces at postgis.refractions.net
[mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of Kai
Carter
Sent: Wednesday, September 23, 2009 6:36 PM
To: postgis-users at postgis.refractions.net
Subject: [postgis-users] SQL moving window averages/statistics

Hi there,

I'm currently have an sql statement that selects a week of descriptive
statistics for various historical weather variables, sorted by date.

SELECT to_char(date, 'MM')||to_char(date, 'DD') as date, max(tmax) as
max_tmax, min(tmax) as min_tmax, avg(tmax) as mean_tmax, stddev(tmax) as
std_tmax, count(tmax) as count_tmax, sum(tmax) as sum_tmax, variance
(tmax) as var_tmax  FROM daily_climate where icao='KSFO' and (EXTRACT (MONTH
from date) =9 and EXTRACT(DAY from date) = 23) or  (EXTRACT (MONTH from
date) = 9 and EXTRACT(DAY from date) = 24) or  (EXTRACT (MONTH from date) =
9 and EXTRACT(DAY from date) = 25) or  (EXTRACT (MONTH from date) = 9 and
EXTRACT(DAY from date) = 26) or  (EXTRACT (MONTH from date) =9 and
EXTRACT(DAY from date) = 27) or  (EXTRACT (MONTH from date) = 9 and
EXTRACT(DAY from date) = 28) or  (EXTRACT (MONTH from date) =  and
EXTRACT(DAY from date) = 29) group by date order by date;

The problem is that I only have 36 years of data to work with, and I would
prefer to have a sample of ~100 rather than 30.  So the idea would be to
have a sample statistics for each day made up of 3 days:
the current day, the day previous and the day after.

Is it possible to get this sort of a result with one select statement?

Kai Carter
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```