mySQL中 实现Oracle 的to_char函数

mySQL中 实现Oracle 的to_char函数，应该可以实现80%的兼容

REPLACE函数是区分大小的

DROP FUNCTION IF EXISTS `to_char`;

CREATE DEFINER = `root`@`localhost` FUNCTION `to_char`(`fdate` datetime,`format` varchar(255))
 RETURNS varchar(255)
BEGIN
	
  DECLARE v_format VARCHAR(100);
	if fdate is null THEN
		RETURN '';
	end if;
	if format is null THEN
		RETURN '';
	end if;

SET v_format=format;
SET v_format = REPLACE(v_format,'hh24','%H');
SET v_format = REPLACE(v_format,'HH24','%H');
SET v_format = REPLACE(v_format,'hh','%H');
SET v_format = REPLACE(v_format,'HH','%H');
SET v_format = REPLACE(v_format,'mi','%i');
SET v_format = REPLACE(v_format,'MI','%i');
SET v_format = REPLACE(v_format,'mI','%i');
SET v_format = REPLACE(v_format,'Mi','%i');
SET v_format = REPLACE(v_format,'ss','%s');
SET v_format = REPLACE(v_format,'SS','%s');
SET v_format = REPLACE(v_format,'YYYY','%Y');
SET v_format = REPLACE(v_format,'yyyy','%Y');
SET v_format = REPLACE(v_format,'MM','%m');
SET v_format = REPLACE(v_format,'mm','%m');
SET v_format = REPLACE(v_format,'DD','%d');
SET v_format = REPLACE(v_format,'dd','%d');

	RETURN DATE_FORMAT(fdate, v_format);
END;