Re: Count dates distinct within an interval - Mailing list pgsql-sql
From | Stuart |
---|---|
Subject | Re: Count dates distinct within an interval |
Date | |
Msg-id | 3F143A73.5060204@blueyonder.co.uk Whole thread Raw |
In response to | Count dates distinct within an interval (Dmitry Tkach <dmitry@openratings.com>) |
List | pgsql-sql |
Dmitry Tkach wrote: > Hi, everybody! > > I was trying to formulate a sql query, that I now think is impossible :-( > I just thought, I'd run it by you before I give up - perhaps, you guys > would have some ideas... > > Suppose, I have a table like this > > create table test > ( > stuff int, > stamp timestamp > ); > > Now, I want to count the occurences of each value of stuff in the table, > but so that entries within 24 hours from each other count as one... > The closest I could think of is: > > select stuff, count (distinct date_trunc ('day', stamp)) from test group > by stuff; > > This doesn't do exactly what I need though - for example, if one entry > is one minute before midnight, and the other one is two minutes later, > they'd get counted as 2, and what I am looking for is the way to get > them collapsed into one as long as they are less then 24 hours apart... > > Now, I am pretty sure, it is simply impossible to do what I want with > count (distinct...) because my 'equality' is not transitive - for > example, three entries, like > A = 2001 - 01- 01 20:20:00 > B = 2001 - 01 - 02 20:19:00 > C = 2001 - 01 - 02 20:21:00 > > Should be counted as *two* (A === B, and B === C, but *not* A === C)... > > Also, I could certainly write a simple function, that would get all the > entries in order, and scan through them, counting according to my rules... > But I was hoping to find some way to do this in plain sql though... > > Any ideas? > > Thanks! > > Dima > You would probably be able to speed the following up using immutable funtions to aid the query, or just a function to do it. However I think this does what you asked in a query. I've put a script at the end. hth, - Stuart -- s is the stuff to group by -- dt is the datetime thing create table Q ( s int4, dt timestamptz); truncate Q; INSERT INTO Q (s,dt) VALUES (1,'2003/01/01'::timestamptz); INSERT INTO Q (s,dt) VALUES (1,'2003/01/02 04:00'::timestamptz); INSERT INTO Q (s,dt) VALUES (1,'2003/01/01 08:00'::timestamptz); INSERT INTO Q (s,dt) VALUES (1,'2003/01/02'::timestamptz); INSERT INTO Q (s,dt) VALUES (1,'2003/01/05 23:00'::timestamptz); INSERT INTO Q (s,dt) VALUES (1,'2003/01/06 22:00'::timestamptz); INSERT INTO Q (s,dt) VALUES (1,'2003/01/07 05:00'::timestamptz); INSERT INTO Q (s,dt) VALUES (3,'2003/01/01'::timestamptz); INSERT INTO Q (s,dt) VALUES (4,'2003/01/01'::timestamptz); INSERT INTO Q (s,dt) VALUES (4,'2003/01/02 05:00'::timestamptz); INSERT INTO Q (s,dt) VALUES (4,'2003/01/03 04:00'::timestamptz); SELECT COUNT(*),s FROM Q WHERE dt IN (SELECT min(R.dt) FROM Q AS R WHERE Q.s=R.s) OR dt IN (SELECT min(P.dt) FROM Q AS P WHERE P.s=Q.s AND P.dt>=date_trunc('day',Q.dt)- CASE WHEN (SELECT max(dt)::time FROM Q AS T WHERE Q.s=T.s AND T.dt<Q.dt AND NOT EXISTS (SELECT * FROM Q AS U WHERE T.dt-'1 day'::interval<U.dt AND T.dt>U.dt AND U.s=Q.s))>Q.dt::time THEN '1 day'::interval ELSE '0 day'::interval END +(SELECT max(dt)::time FROM Q AS T WHERE Q.s=T.s AND T.dt<Q.dt AND NOT EXISTS (SELECT * FROM Q AS U WHERE T.dt-'1 day'::interval<U.dt AND T.dt>U.dt AND U.s=Q.s))) GROUP BY s;