MySQL字符串按照数值排序方式

SELECT * FROM test_21 a ORDER BY a.testId desc;

SELECT * FROM test_21 a ORDER BY a.testId+0 desc;
SELECT * FROM test_21 a ORDER BY a.testId-2 desc;
SELECT * FROM test_21 a ORDER BY a.testId*1 desc;
SELECT * FROM test_21 a ORDER BY a.testId/4 desc;

SELECT * FROM test_21 a ORDER BY cast(a.testId as SIGNED) desc;
SELECT * FROM test_21 a ORDER BY convert(a.testId,SIGNED) desc;

CAST(expr AS type)
CONVERT(expr,type)

CREATE TABLE `s_menu` (
  `ID` int(11) NOT NULL AUTO_INCREMENT,
  `PARENT_ID` int(11) DEFAULT NULL,
  `ORDER` varchar(5) DEFAULT NULL,
  `MENU_NAME` varchar(255) DEFAULT NULL,
  `MENU_URL` varchar(255) DEFAULT NULL,
  `MENU_ICON` varchar(100) DEFAULT NULL,
  `SORT_NUM` int(2) DEFAULT NULL,
  `IS_SHOW` int(2) DEFAULT NULL,
  `PERMISSION` varchar(100) DEFAULT NULL,
  `LOGIN_TYPE` int(11) DEFAULT NULL COMMENT '0:WEB,1:PC,2:APP',
  `CREATE_BY` int(11) DEFAULT NULL,
  `CREATE_DATE` date DEFAULT NULL,
  `MEMO` varchar(1000) DEFAULT NULL,
  PRIMARY KEY (`ID`)
) ENGINE=InnoDB AUTO_INCREMENT=254 DEFAULT CHARSET=utf8 COMMENT='菜单';

SELECT
  `ID`,
  `PARENT_ID` ,
  `ORDER` ,
  `MENU_NAME`,
  `MENU_URL` ,
  `MENU_ICON` ,
  `SORT_NUM` ,
  `IS_SHOW` ,
  `PERMISSION` ,
  `LOGIN_TYPE` ,
  `CREATE_BY` ,
  `CREATE_DATE`,
  `MEMO` 
FROM
    s_menu
ORDER BY
      (s_menu.ORDER+0) ASC

SELECT
  `ID`,
  `PARENT_ID` ,
  `ORDER` ,
  `MENU_NAME`,
  `MENU_URL` ,
  `MENU_ICON` ,
  `SORT_NUM` ,
  `IS_SHOW` ,
  `PERMISSION` ,
  `LOGIN_TYPE` ,
  `CREATE_BY` ,
  `CREATE_DATE`,
  `MEMO` 
FROM
    s_menu
ORDER BY
      cast (s_menu.ORDER as SIGNED) ASC