PostgreSQL实现dateadd函数

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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 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 时间运算间隔，整型，正负均可
  
• $3 本地时间，常用now()代替
  

　　范例：
　　


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