원본출처 : http://www.brasileiro.net/postgres/cookbook/view-one-recipe.adp?recipe_id=193

Submitted on: 04-24-2001

Description:

Make sure this semester doesn't overlap at all with any previously-entered semesters. Used in a CHECK clause for the table.

Code:

-- joel burton (jburton@scw.org)

-- public domain

CREATE FUNCTION "sem_nooverlap" (character varying,date,date) RETURNS boolean AS '

declare

mySemCode alias for $1;

myStart alias for $2;

myEnd alias for $3;

begin

RETURN ( not EXISTS

(SELECT * from tlkpSem where SemCode <> mySemCode AND

( myStart BETWEEN SemStart AND SemEnd

OR myEnd BETWEEN SemStart AND SemEnd ) )

);

END;' LANGUAGE 'plpgsql';