Sum up network events by type, interval and network

Hi all,

For each event of each type in each interval I want to compute the sum  
of events referencing the same relayNet (via host) and insert/update 1  
row in SumOfEvents.
All intervals start at a time, minimum 5 minutes in the past, rounded  
down modulo 5 minutes like:

SELECT DATE_TRUNC('MINUTES', NOW () - ('0:' || (SELECT  
(EXTRACT('MINUTE' FROM NOW())::INT % 5) + 5 ) || ':0')::INTERVAL);



CREATE TABLE host (
   id            SERIAL  PRIMARY KEY,
   relayNetFK    INT
                 REFERENCES relayNet
                         ON DELETE CASCADE
)

CREATE TABLE event (
   id            SERIAL  PRIMARY KEY,
   type          CHAR         NOT NULL
                 CHECK ( type IN ('C', 'A', 'D', 'S', 'R') ),
   timeOfEvent   timestamp       NOT NULL
                         DEFAULT NOW(),
   hostfk        INT          NOT NULL
                 REFERENCES host
                         ON DELETE CASCADE
)

CREATE TABLE relayNet (
   id            SERIAL  PRIMARY KEY,
   name          TEXT            NOT NULL UNIQUE
)

CREATE TYPE eventIntervals AS ENUM ('5m', '30m', '3h', '24h', '30d');
CREATE TABLE SumOfEvents (
   id            SERIAL  PRIMARY KEY,
   type          CHAR         NOT NULL
                 CHECK ( type IN ('C', 'A', 'D', 'S', 'R') ),
   startTime     timestamp       NOT NULL,
   interval      eventIntervals  NOT NULL,
   value         INT,        -- sum
   relayNetFK    INT
                 REFERENCES relayNet
                         ON DELETE CASCADE,

   UNIQUE (type, interval, relayNetFK)
)

Can this be done w/o procedural code?
Any hints?

Thanks, Axel
---
axel.rau@chaos1.de  PGP-Key:29E99DD6  +49 151 2300 9283  computing @  
chaos claudius