원본출처 : http://www.brasileiro.net/postgres/cookbook/view-one-recipe.adp?recipe_id=21

Submitted on: 03-16-2001

Description:

Simple functions to add/subtract dates. Prototypes: DATE_ADD(DATE,INT,PERIOD) DATE_SUB(DATE,INT,PERIOD) Where PERIOD is one of 'DAYS','MONTHS',or 'YEARS'. examples: SELECT DATE_ADD('1999-12-31',1,'DAYS') will produce '2001-01-01'

Code:

-- DATE_ADD, DATE_SUB date manipulation functions

-- Copyright (C) 2001 Mark Steele (msteele@inet-interactif.com)

--

-- This program is free software; you can redistribute it and/or

-- modify it under the terms of the GNU General Public License

-- as published by the Free Software Foundation; either version 2

-- of the License, or (at your option) any later version.

--

-- This program is distributed in the hope that it will be useful,

-- but WITHOUT ANY WARRANTY; without even the implied warranty of

-- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the

-- GNU General Public License for more details.

--

-- You should have received a copy of the GNU General Public License

-- along with this program; if not, write to the Free Software

-- Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.

CREATE FUNCTION DATE_ADD(date,int4,text) RETURNS DATE AS '

DECLARE

var1 date;

var2 text;

BEGIN

var2 = $2 || '' '' || $3;

SELECT INTO var1

to_date($1 + var2::interval, ''YYYY-MM-DD'');

RETURN var1;

END;' LANGUAGE 'plpgsql';

CREATE FUNCTION DATE_SUB(date,int4,text) RETURNS DATE AS '

DECLARE

var1 date;

var2 text;

BEGIN

var2 = $2 || '' '' || $3;

SELECT INTO var1

to_date($1 - var2::interval, ''YYYY-MM-DD'');

RETURN var1;

END;' LANGUAGE 'plpgsql';