Postgresql兼容Oracle改造系列——时间函数ROUND (date)

背景描述

Postgresql中不支持round(date)函数，使用plpgsql做补齐。

原理与解决方案

Oracle中round(date)实现的功能是四舍五入到指定的单位上。

在Postgresql中使用date_trunc，但是只能把时间做截断，所以在实现时需要先做偏移再做截断，实现四舍五入的效果。

date_trunc(text, timestamp)	
return: timestamp

实现

CREATE OR REPLACE FUNCTION round(timestamp, text) 
RETURNS timestamp AS 
$m$
DECLARE 
  r timestamp; 
BEGIN
  IF $2 = 'minute' THEN
    SELECT date_trunc($2, $1 + interval '30 second') INTO r;
  ELSIF $2 = 'hour' THEN
    SELECT date_trunc($2, $1 + interval '30 minute') INTO r;
  ELSIF $2 = 'day' THEN
    SELECT date_trunc($2, $1 + interval '12 hour') INTO r;
  ELSIF $2 = 'week' THEN
    SELECT date_trunc($2, $1 + interval '84 hour') INTO r;
  ELSIF $2 = 'month' THEN
    SELECT date_trunc($2, $1 + interval '15 day') INTO r;
  ELSIF $2 = 'year' THEN
    SELECT date_trunc($2, $1 + interval '6 month') INTO r;
  ELSE
    RAISE EXCEPTION 'timestamp units "%" not recognized, please contact DBA', $2;
  END IF;
  RETURN r;
END;
$m$ LANGUAGE plpgsql;

效果

select round(timestamp '2015-07-10 11:52:30.000', 'year');
2016-01-01 00:00:00


select round(timestamp '2015-07-10 11:52:30.000', 'hour');
2015-07-10 12:00:00


select round(timestamp '2015-07-10 11:52:30.000', 'minute');
2015-07-10 11:53:00