SELECT 1+(SELECT COUNT( DISTINCT 平均成绩) FROM (SELECT sid,AVG(score) AS 平均成绩 FROM sc GROUP BY sid ) AS T1 WHERE 平均成绩 > T2.平均成绩) as 名次, sid as 学生学号,平均成绩 FROM (SELECT sid,AVG(score) 平均成绩 FROM sc GROUP BY sid ) AS T2 ORDER BY 平均成绩 desc 什么意思
时间: 2024-04-16 07:24:54 浏览: 95
这是一个SQL查询语句,用于计算每个学生的平均成绩,并按照平均成绩进行降序排序。查询结果包括学生的名次、学号和平均成绩。
具体的查询逻辑如下:
1. 内层子查询 T1:计算每个学生的平均成绩,并筛选出平均成绩高于 T2.平均成绩的学生。使用 DISTINCT 关键字去除重复的平均成绩。
2. 外层主查询 T2:计算每个学生的平均成绩,并将内层子查询的结果作为条件,统计高于自己平均成绩的学生数量,作为该学生的名次。
3. 最终的结果按照平均成绩进行降序排序,包括名次、学生学号和平均成绩。
请注意,这只是对查询语句的解释,具体的结果和意义还需要根据实际数据来分析。
相关问题
MySQL以数据库user_db及数据表student、teacher、class、course、sc为基础(11)查询选修“数据库原理”的学生的最高成绩、最低成绩、平均成绩; (12)查询平均成绩在60分以上的课程及其平均成绩; (13)查询平均成绩大于“高莉”的平均成绩的学生学号、姓名及平均成绩; (14)查询每门课程中成绩最低的学生的学号、姓名、性别、院系; (15)查询只被一名学生选修的课程的课程号、课程名。
11.
```
SELECT MAX(score) AS max_score, MIN(score) AS min_score, AVG(score) AS avg_score
FROM sc
WHERE course_name = '数据库原理';
```
12.
```
SELECT course_id, course_name, AVG(score) AS avg_score
FROM sc
GROUP BY course_id, course_name
HAVING AVG(score) > 60;
```
13.
```
SELECT s.stu_id, s.stu_name, AVG(score) AS avg_score
FROM student s, sc c
WHERE s.stu_id = c.stu_id
GROUP BY s.stu_id, s.stu_name
HAVING AVG(score) > (SELECT AVG(score) FROM sc WHERE stu_name = '高莉');
```
14.
```
SELECT s.stu_id, s.stu_name, s.gender, s.department, c.course_name, MIN(score) AS min_score
FROM student s, sc c
WHERE s.stu_id = c.stu_id
AND score = (SELECT MIN(score) FROM sc WHERE course_name = c.course_name)
GROUP BY c.course_name, s.stu_id, s.stu_name, s.gender, s.department;
```
15.
```
SELECT course_id, course_name
FROM sc
GROUP BY course_id, course_name
HAVING COUNT(DISTINCT stu_id) = 1;
```
MySQL以数据库user_db及数据表student、teacher、class、course、sc为基础(11)查询信息技术学院的必修课和限选课的数量及平均学分; (12)查询每名学生的选课数量及平均成绩,按照平均成绩降序排列; (13)查询各门课程编号、选课人数及其及格率; (14)查询选课人数前五名的课程; (15)查询选修课程数最多和最少的学生的学号及选课数; 2、SQL子查询的应用; (1)查询信息技术学院年龄最大的学生的学号、姓名、性别; (2)查询每个院系年龄最大的学生的学号、姓名、性别、院系及年龄; (3)查询和“崔晓”一个院系的其他学生的学号、姓名、院系; (4)查询平均成绩在60分以上的课程及其平均成绩; (5)查询平均成绩大于“高莉”的平均成绩的学生学号、姓名及平均成绩; (6)查询课程的学分高于全体课程平均学分的课程编号、名称、学分及所属院系,查询结果按照学分降序排列; (7)查询至少有一名学生选修的所有课程的课程号及课程名;
11. 查询信息技术学院的必修课和限选课的数量及平均学分:
```
SELECT
SUM(CASE WHEN course_type = '必修' THEN 1 ELSE 0 END) AS required_course_count,
SUM(CASE WHEN course_type = '限选' THEN 1 ELSE 0 END) AS elective_course_count,
AVG(CASE WHEN course_type IN ('必修', '限选') THEN credit END) AS avg_credit
FROM
class
WHERE
department = '信息技术学院';
```
12. 查询每名学生的选课数量及平均成绩,按照平均成绩降序排列:
```
SELECT
sc.student_id,
COUNT(*) AS course_count,
AVG(score) AS avg_score
FROM
sc
JOIN
student ON student.id = sc.student_id
GROUP BY
sc.student_id
ORDER BY
avg_score DESC;
```
13. 查询各门课程编号、选课人数及其及格率:
```
SELECT
course_id,
COUNT(*) AS student_count,
SUM(CASE WHEN score >= 60 THEN 1 ELSE 0 END) / COUNT(*) AS pass_rate
FROM
sc
GROUP BY
course_id;
```
14. 查询选课人数前五名的课程:
```
SELECT
course_id,
COUNT(*) AS student_count
FROM
sc
GROUP BY
course_id
ORDER BY
student_count DESC
LIMIT 5;
```
15. 查询选修课程数最多和最少的学生的学号及选课数:
```
SELECT
student_id,
COUNT(*) AS course_count
FROM
sc
GROUP BY
student_id
HAVING
COUNT(*) = (SELECT MAX(cnt) FROM (SELECT COUNT(*) AS cnt FROM sc GROUP BY student_id) AS t)
OR COUNT(*) = (SELECT MIN(cnt) FROM (SELECT COUNT(*) AS cnt FROM sc GROUP BY student_id) AS t);
```
1. SQL子查询的应用:
(1) 查询信息技术学院年龄最大的学生的学号、姓名、性别:
```
SELECT
id, name, gender
FROM
student
WHERE
department = '信息技术学院' AND age = (SELECT MAX(age) FROM student WHERE department = '信息技术学院');
```
(2) 查询每个院系年龄最大的学生的学号、姓名、性别、院系及年龄:
```
SELECT
s.id, s.name, s.gender, s.age, s.department
FROM
student s
JOIN
(SELECT department, MAX(age) AS max_age FROM student GROUP BY department) t
ON
s.department = t.department AND s.age = t.max_age;
```
(3) 查询和“崔晓”一个院系的其他学生的学号、姓名、院系:
```
SELECT
id, name, department
FROM
student
WHERE
department = (SELECT department FROM student WHERE name = '崔晓') AND name != '崔晓';
```
(4) 查询平均成绩在60分以上的课程及其平均成绩:
```
SELECT
course_id,
AVG(score) AS avg_score
FROM
sc
WHERE
course_id IN (SELECT course_id FROM sc GROUP BY course_id HAVING AVG(score) >= 60)
GROUP BY
course_id;
```
(5) 查询平均成绩大于“高莉”的平均成绩的学生学号、姓名及平均成绩:
```
SELECT
id, name, AVG(score) AS avg_score
FROM
student
JOIN
sc ON student.id = sc.student_id
WHERE
AVG(score) > (SELECT AVG(score) FROM student JOIN sc ON student.id = sc.student_id WHERE name = '高莉')
GROUP BY
id, name;
```
(6) 查询课程的学分高于全体课程平均学分的课程编号、名称、学分及所属院系,查询结果按照学分降序排列:
```
SELECT
course.id, course.name, course.credit, course.department
FROM
course
WHERE
credit > (SELECT AVG(credit) FROM course)
ORDER BY
credit DESC;
```
(7) 查询至少有一名学生选修的所有课程的课程号及课程名:
```
SELECT
id, name
FROM
course
WHERE
id IN (SELECT DISTINCT course_id FROM sc);
```
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