To: pgsql-sql@postgresql.org
From: Wolfgang Meiners <WolfgangMeiners01@web.de>
Subject: check for overlapping time intervals
Date: Mon, 22 Apr 2013 12:19:17 +0200
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Hi,

I am on postgresql 9.1 and use at table like

CREATE TABLE timetable(
 tid   INTEGER PRIMARY KEY,
 gid   INTEGER REFERENCES groups(gid),
 day   DATE,
 s     TIME NOT NULL, --- start
 e     TIME NOT NULL, --- end
 CHECK (e > s));

Now, i need a constraint to prevent overlapping timeintervals in this
table. For this, i use a trigger:

CREATE OR REPLACE FUNCTION validate_timetable() RETURNS trigger AS $$
BEGIN
 IF TG_OP = 'INSERT' THEN
  IF EXISTS(
   SELECT * FROM timetable
   WHERE gid = NEW.gid AND day = NEW.day
   AND s < NEW.e AND e > NEW.s)
   THEN
    RAISE EXCEPTION 'overlapping intervals';
   END IF;
 ELSIF TG_OP = 'UPDATE' THEN
  IF EXISTS(
   SELECT * FROM timetable
   WHERE gid = NEW.gid AND day = NEW.day
   AND tid <> OLD. tid
   AND s < NEW.e AND e > NEW.s)
   THEN
    RAISE EXCEPTION 'overlapping intervals';
   END IF;
 END IF;
 RETURN NEW;
END; $$ LANGUAGE plpgsql;

CREATE TRIGGER validate_timetable
BEFORE INSERT OR UPDATE ON timetable
FOR EACH ROW EXECUTE PROCEDURE
validate_timetable();

Is there a simpler way to check for overlapping timeintervals? I ask
this question, because i have more similar tables with similar layout
and would have to write similar functions again and again.

Thank you for any hints
Wolfgang


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