简单描述：
成绩表中有学生姓名、学生科目以及学生分数。查询分数最高和分数最低的学生的以及学生的分数。注意的点如下：

1、group by，select 选择的列，必须是group by 中的列，或者是函数形式。
2、利用MAX（） 和MIN（）sql函数。
3、建立的表结构如下。

-- ----------------------------
-- Table structure for grade
-- ----------------------------
DROP TABLE IF EXISTS `grade`;
CREATE TABLE `grade` (
  `stu_name` varchar(255) NOT NULL,
  `stu_subject` varchar(255) NOT NULL,
  `score` int(255) DEFAULT NULL,
  PRIMARY KEY (`stu_subject`,`stu_name`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1;

-- ----------------------------
-- Records of grade
-- ----------------------------
INSERT INTO `grade` VALUES ('lilei', 'shuxue', '99');
INSERT INTO `grade` VALUES ('xiaoyong', 'shuxue', '66');
INSERT INTO `grade` VALUES ('lilei', 'yingyu', '80');
INSERT INTO `grade` VALUES ('xiaoyong', 'yingyu', '55');
INSERT INTO `grade` VALUES ('lilei', 'yuwen', '78');
INSERT INTO `grade` VALUES ('xiaoyong', 'yuwen', '88');

思路
1)按照科目分组查询成绩最高的人
SELECT grade.stu_subject, MAX(grade.score) as score from grade GROUP BY stu_subject;
2)显示出成绩最高的人的姓名和科目名称
SELECT grade.* from grade,
(SELECT grade.stu_subject, MAX(grade.score) as score from grade GROUP BY stu_subject )b
WHERE grade.score = b.score and grade.stu_subject = b.stu_subject;
3)显示出列标题.
SELECT “成绩最高”,grade.* from grade,
(SELECT grade.stu_subject, MAX(grade.score) as score from grade GROUP BY stu_subject )b
WHERE grade.score = b.score and grade.stu_subject = b.stu_subject;

成绩最低的也是如此就是利用MIN()函数, 如果需要同时查出, 可以用union 如下sql

SELECT "成绩最高",grade.* from grade, 
(SELECT  grade.stu_subject, MAX(grade.score) as score  from grade GROUP BY  stu_subject  )b
WHERE grade.score = b.score and grade.stu_subject = b.stu_subject
UNION
SELECT "成绩最低",grade.* from grade, 
(SELECT  grade.stu_subject, MIN(grade.score) as score  from grade GROUP BY  stu_subject  )b
WHERE grade.score = b.score and grade.stu_subject = b.stu_subject;

查询结果如下图所示:

总结:
路漫漫其修远兮,吾将上下而求索。