SQL查询成绩表中的每科第三名

SQL查询成绩表中的每科第三名

　题目要求

　表格数据

• grade表

c_id	c_no	c_name
1	1	80
1	2	90
1	3	70
1	4	95
2	1	64
2	2	88
2	3	89
2	4	79
3	1	90
3	2	80
3	3	96
3	4	85
4	1	88
4	2	90
4	3	50
4	4	60

• course表

c_id	c_no	c_name
1	001	C/C++
2	002	JAVA
3	003	Linux
4	004	数据库

1. student表

s_id	s_no	s_name
1	001	gb
2	002	lly
3	003	pdl
4	004	lb

解题过程

• 第一步 先根据成绩表得出每科每名学生的排名

查询代码

SELECT
    t1.*, (
        SELECT
            count(*)
        FROM
            grade t2
        WHERE
            t1.score <= t2.score
        AND t1.c_id = t2.c_id
    ) AS rownum
FROM
    grade t1

查询结果

c_id	s_id	score	rownum
1	1	80	3
1	2	90	2
1	3	70	4
1	4	95	1
2	1	64	4
2	2	88	2
2	3	89	1
2	4	79	3
3	1	90	2
3	2	80	4
3	3	96	1
3	4	85	3
4	1	88	2
4	2	90	1
4	3	50	4

• 第二步 将第一步所的表命名为t3 然后将表中rownum为3的查询出来 并按学科排序

查询代码

SELECT
    *
FROM
    (
        SELECT
            t1.*, (
                SELECT
                    count(*)
                FROM
                    grade t2
                WHERE
                    t1.score <= t2.score
                AND t1.c_id = t2.c_id
            ) AS rownum
        FROM
            grade t1
    ) t3
WHERE
    rownum = 3
ORDER BY
    c_id

查询结果

c_id	s_id	score	rownum
1	1	80	3
2	4	79	3
3	4	85	3
4	4	60	3

• 第三步 对最终查询结果与 student cource 两表进行左连接

查询代码

SELECT
    student.s_no,
    student.s_name,
    course.c_name,
    grade_temp.score
FROM
    (
        SELECT
            *
        FROM
            (
                SELECT
                    t1.*, (
                        SELECT
                            count(*)
                        FROM
                            grade t2
                        WHERE
                            t1.score <= t2.score
                        AND t1.c_id = t2.c_id
                    ) AS rownum
                FROM
                    grade t1
            ) t3
        WHERE
            rownum = 3
        ORDER BY
            c_id,
            score DESC
    ) grade_temp
LEFT JOIN course ON grade_temp.c_id = course.c_id
LEFT JOIN student ON grade_temp.s_id = student.s_id

查询结果

s_id	s_name	c_name	score
001	gb	C/C++	80
004	lb	JAVA	79
004	lb	Linux	85
004	lb	数据库	60

附上表结构和表数据sql

SET FOREIGN_KEY_CHECKS=0;

-- ----------------------------
-- Table structure for course
-- ----------------------------
DROP TABLE IF EXISTS `course`;
CREATE TABLE `course` (
  `c_id` int(11) NOT NULL,
  `c_no` varchar(20) NOT NULL,
  `c_name` varchar(255) NOT NULL
) ENGINE=MyISAM DEFAULT CHARSET=utf8;

-- ----------------------------
-- Records of course
-- ----------------------------
INSERT INTO `course` VALUES ('1', '001', 'C/C++');
INSERT INTO `course` VALUES ('2', '002', 'JAVA');
INSERT INTO `course` VALUES ('3', '003', 'Linux');
INSERT INTO `course` VALUES ('4', '004', '数据库');

-- ----------------------------
-- Table structure for grade
-- ----------------------------
DROP TABLE IF EXISTS `grade`;
CREATE TABLE `grade` (
  `c_id` int(11) NOT NULL,
  `s_id` int(11) NOT NULL,
  `score` float NOT NULL
) ENGINE=MyISAM DEFAULT CHARSET=utf8;

-- ----------------------------
-- Records of grade
-- ----------------------------
INSERT INTO `grade` VALUES ('1', '1', '80');
INSERT INTO `grade` VALUES ('1', '2', '90');
INSERT INTO `grade` VALUES ('1', '3', '70');
INSERT INTO `grade` VALUES ('1', '4', '95');
INSERT INTO `grade` VALUES ('2', '1', '64');
INSERT INTO `grade` VALUES ('2', '2', '88');
INSERT INTO `grade` VALUES ('2', '3', '89');
INSERT INTO `grade` VALUES ('2', '4', '79');
INSERT INTO `grade` VALUES ('3', '1', '90');
INSERT INTO `grade` VALUES ('3', '2', '80');
INSERT INTO `grade` VALUES ('3', '3', '96');
INSERT INTO `grade` VALUES ('3', '4', '85');
INSERT INTO `grade` VALUES ('4', '1', '88');
INSERT INTO `grade` VALUES ('4', '2', '90');
INSERT INTO `grade` VALUES ('4', '3', '50');
INSERT INTO `grade` VALUES ('4', '4', '60');

-- ----------------------------
-- Table structure for student
-- ----------------------------
DROP TABLE IF EXISTS `student`;
CREATE TABLE `student` (
  `s_id` int(11) NOT NULL,
  `s_no` varchar(20) NOT NULL,
  `s_name` varchar(255) NOT NULL
) ENGINE=MyISAM DEFAULT CHARSET=utf8;

-- ----------------------------
-- Records of student
-- ----------------------------
INSERT INTO `student` VALUES ('1', '001', 'gb');
INSERT INTO `student` VALUES ('2', '002', 'lly');
INSERT INTO `student` VALUES ('3', '003', 'pdl');
INSERT INTO `student` VALUES ('4', '004', 'lb');