MySQL使用IF语句及用case语句对条件并结果进行判断 

CREATE TABLE `t1` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `name` varchar(255) DEFAULT NULL,
  `jgid` int(11) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=8 DEFAULT CHARSET=utf8;

INSERT INTO `avlicy`.`t1`(`id`, `name`, `jgid`) VALUES (1, '二二', 2);
INSERT INTO `avlicy`.`t1`(`id`, `name`, `jgid`) VALUES (2, '李四', 2);
INSERT INTO `avlicy`.`t1`(`id`, `name`, `jgid`) VALUES (4, '七七', 3);
INSERT INTO `avlicy`.`t1`(`id`, `name`, `jgid`) VALUES (5, '小猕猴', 1);
INSERT INTO `avlicy`.`t1`(`id`, `name`, `jgid`) VALUES (6, '小米粥', 1);
INSERT INTO `avlicy`.`t1`(`id`, `name`, `jgid`) VALUES (7, '小哈吧', 1);

SELECT
	t1.*,
	IF(MOD(t1.id,2)=0 ,'是','否') AS 是否被二整除
FROM
	t1

SELECT
	t1.* 
FROM
	t1 
WHERE
IF( MOD ( t1.id, 2 )= 0, id = jgid, id <> jgid )

SELECT
	*,
 CASE
		WHEN jgid = 1 THEN
		'学生' 
		WHEN jgid = 2 THEN
		'教师' 
		WHEN jgid = 3 THEN
		'家长' ELSE '' 
	END AS '角色' 
FROM
	t1