PostgreSQL实现dateadd函数

CREATE OR REPLACE FUNCTION timeadd(difftype character varying, incrementvalue integer, inputdate timestamp with time zone)
  RETURNS timestamp without time zone AS
$BODY$
DECLARE
   YEAR_CONST Char(15) := 'year';
   MONTH_CONST Char(15) := 'month';
   WEEK_CONST Char(15) := 'week';
   DAY_CONST Char(15) := 'day';
   HOUR_CONST Char(15) := 'hour';
   MIN_CONST Char(15) :='mi';
   SECOND_CONST Char(15) :='ss';
   dateTemp timestamp;
   intervals interval;
BEGIN
   IF lower($1) = lower(YEAR_CONST) THEN
       select cast(cast(incrementvalue as character varying) || ' year' as interval) into intervals;
   ELSEIF lower($1) = lower(MONTH_CONST) THEN
       select cast(cast(incrementvalue as character varying) || ' months' as interval) into intervals;
   ELSEIF lower($1) = lower(WEEK_CONST) THEN
       select cast(cast(incrementvalue as character varying) || ' week' as interval) into intervals;
   ELSEIF lower($1) = lower(DAY_CONST) THEN
       select cast(cast(incrementvalue as character varying) || ' day' as interval) into intervals;
   ELSEIF lower($1) = lower(HOUR_CONST) THEN
       select cast(cast(incrementvalue as character varying) || ' hour' as interval) into intervals;
   ELSEIF lower($1) = lower(MIN_CONST) THEN
       select cast(cast(incrementvalue as character varying) || ' minute' as interval) into intervals;
   ELSEIF lower($1) = lower(SECOND_CONST) THEN
       select cast(cast(incrementvalue as character varying) || ' second' as interval) into intervals;   
   END IF;

   dateTemp:= inputdate + intervals;

   RETURN dateTemp;
END;
$BODY$
  LANGUAGE 'plpgsql' VOLATILE;

 

------------------------------------------- API ------------------------------------------------------------

功能：类似于Sybase语法中的dateadd函数，用于时间加减相应的时间段

参数：

1. $1 时间运算格式，分为：ss（秒）,mi（分钟）,hour（小时）,day（天）,week（周）,month（月）,year（年）
2. $2 时间运算间隔，整型，正负均可
3. $3 本地时间，常用now()代替

范例：

select timeadd('day',-1,now())