CREATE OR REPLACE FUNCTION datestr_to_timestamp(datestr VARCHAR)
  RETURNS BIGINT AS
$BODY$
	--由日期字符串格式为2011-12-05 19:10:00转换成long:1323083400 * 1000
	--由于可能会出现传入参数带秒，故这里都将秒舍去
DECLARE
	result BIGINT;
BEGIN
	result := extract(epoch FROM date_trunc('minute',to_timestamp(datestr,'YYYY-MM-DD HH24:MI:SS')));
	RETURN result * 1000;
END;
$BODY$
  LANGUAGE 'plpgsql' VOLATILE;

CREATE OR REPLACE FUNCTION timestamp_to_datestr(date BIGINT)
  RETURNS VARCHAR AS
$BODY$
	--由时间戳转换成日期字符串 参数形如：1323083400000 转换后为2011-12-05 19:10:00
DECLARE
	result VARCHAR;
BEGIN
	result := to_char(to_timestamp(date/1000),'YYYY-MM-DD HH24:MI:SS');
	RETURN result;
END;
$BODY$
  LANGUAGE 'plpgsql' VOLATILE;

调用示例：
select datestr_to_timestamp('2011-12-05 19:10:00');
select timestamp_to_datestr(1323083400000);