用sql（Oracle）语句实现：[右外连接] 查询课程的选课情况（未选课程的课号和成绩为空）

假设有两张表：课程表（course）和选课表（selection），其中课程表包含课程号（cid）和课程名称（cname），选课表包含学生号（sid）、课程号（cid）和成绩（score）三个字段。

以下是实现右外连接查询课程的选课情况的 Oracle SQL 语句：

SELECT c.cid, c.cname, s.sid, s.score
FROM course c
RIGHT OUTER JOIN selection s
ON c.cid = s.cid
ORDER BY c.cid;

解释：

1. 使用 RIGHT OUTER JOIN 实现右外连接，将选课表作为主表，课程表作为从表。

2. ON 子句中使用 cid 字段进行关联。

3. 查询结果包括课程表的课程号和课程名称，以及选课表的学生号和成绩。

4. 如果某个课程没有学生选，对应的学生号和成绩字段值为空。

5. 使用 ORDER BY 子句按课程号排序。

相关问题

sql（Oracle）语句查询每门课号的选课人数。（无学生的课程为0） 右连接，选课表有空值 选课表(sc)包括学号，课程号和成绩 课程表(c)包括课程号，课程名，学分

可以使用以下SQL语句查询每门课号的选课人数：

SELECT c.课程号, COUNT(sc.学号) AS 选课人数 
FROM 课程表 c 
RIGHT JOIN 选课表 sc ON c.课程号 = sc.课程号 
GROUP BY c.课程号 
ORDER BY c.课程号;

其中，使用了右连接（RIGHT JOIN）来保证即使没有学生选修某门课程，该课程也会被显示出来，并且将选修该门课程的学生数量作为结果展示。使用了COUNT函数来计算选修每门课程的学生数量，GROUP BY语句来对结果按照课程号进行分组，ORDER BY语句来按照课程号进行升序排列。

以下查询请尽量多使用不同的SQL语句实现! (1）选择数据库JX; (2)查询选修了“3”号课程且成绩在70分以上的学生信息; (3）查询所有不比“电子工程”系的所有学生年龄大的其他系的学生信息; (4)查询选修了“3”号课程的学生姓名、成绩及任课教师姓名; (5）查询开设的课程中选课人数不足15人的课程号及人数信息; (6）查询选修课程数低于3门的学生信息; (7）查询没有选修课程的同学的基本信息; (8）查询既选修了“3”号又选修了“4”号课程的学生姓名、课程名及成绩; (9)查询同时选修了“操作系统”课程和“数据库原理”课程的学生名单; (10）查询所有同学的基本信息及选课情况（包含未选课同学的信息); (11）列出所有参加了数据库课程考试的学生姓名和成绩; (12）查询所有学生和教师的姓名（允许重名）并标识类型（学生/老师); (13）查询每一课程的间接选修课，以“课程名”、“间接选修课名”作列名; (14）列出所有没有选修“数据结构”课程的学生的学号、姓名、所在院系。

1. 使用MySQL语句：
(1) USE JX;
(2) SELECT * FROM student WHERE s_id IN (SELECT s_id FROM score WHERE c_id = 3 AND score >= 70);
(3) SELECT * FROM student WHERE age > (SELECT MAX(age) FROM student WHERE department != '电子工程');
(4) SELECT student.s_name, score.score, teacher.t_name FROM student LEFT JOIN score ON student.s_id = score.s_id LEFT JOIN course ON score.c_id = course.c_id LEFT JOIN teacher ON course.t_id = teacher.t_id WHERE score.c_id = 3;
(5) SELECT c_id, COUNT(*) AS num FROM score GROUP BY c_id HAVING num < 15;
(6) SELECT student.s_id, student.s_name FROM student LEFT JOIN score ON student.s_id = score.s_id GROUP BY student.s_id HAVING COUNT(*) < 3;
(7) SELECT * FROM student WHERE s_id NOT IN (SELECT s_id FROM score);
(8) SELECT student.s_name, course.c_name, score.score FROM student LEFT JOIN score ON student.s_id = score.s_id LEFT JOIN course ON score.c_id = course.c_id WHERE score.c_id IN (3,4);
(9) SELECT student.s_name FROM student LEFT JOIN score ON student.s_id = score.s_id LEFT JOIN course ON score.c_id = course.c_id WHERE course.c_name = '操作系统' AND student.s_id IN (SELECT student.s_id FROM student LEFT JOIN score ON student.s_id = score.s_id LEFT JOIN course ON score.c_id = course.c_id WHERE course.c_name = '数据库原理');
(10) SELECT student.s_id, student.s_name, student.department, course.c_id, course.c_name, score.score FROM student LEFT JOIN score ON student.s_id = score.s_id RIGHT JOIN course ON score.c_id = course.c_id;
(11) SELECT student.s_name, score.score FROM student LEFT JOIN score ON student.s_id = score.s_id LEFT JOIN course ON score.c_id = course.c_id WHERE course.c_name = '数据库';
(12) SELECT s_name AS name, '学生' AS type FROM student UNION SELECT t_name AS name, '老师' AS type FROM teacher;
(13) SELECT course.c_name AS course, indirect_course.c_name AS indirect_course FROM course LEFT JOIN indirect_course ON course.c_id = indirect_course.c_id;
(14) SELECT student.s_id, student.s_name, student.department FROM student WHERE student.s_id NOT IN (SELECT s_id FROM score WHERE c_id = 2);

2. 使用Oracle语句：
(1) ALTER SESSION SET current_schema = JX;
(2) SELECT * FROM student WHERE s_id IN (SELECT s_id FROM score WHERE c_id = 3 AND score >= 70);
(3) SELECT * FROM student WHERE age > (SELECT MAX(age) FROM student WHERE department != '电子工程');
(4) SELECT student.s_name, score.score, teacher.t_name FROM student, score, course, teacher WHERE student.s_id = score.s_id AND score.c_id = course.c_id AND course.t_id = teacher.t_id AND score.c_id = 3;
(5) SELECT c_id, COUNT(*) AS num FROM score GROUP BY c_id HAVING COUNT(*) < 15;
(6) SELECT student.s_id, student.s_name FROM student, score WHERE student.s_id = score.s_id GROUP BY student.s_id HAVING COUNT(*) < 3;
(7) SELECT * FROM student WHERE s_id NOT IN (SELECT s_id FROM score);
(8) SELECT student.s_name, course.c_name, score.score FROM student, score, course WHERE student.s_id = score.s_id AND score.c_id = course.c_id AND score.c_id IN (3,4);
(9) SELECT student.s_name FROM student, score, course WHERE student.s_id = score.s_id AND score.c_id = course.c_id AND course.c_name = '操作系统' AND student.s_id IN (SELECT student.s_id FROM student, score, course WHERE student.s_id = score.s_id AND score.c_id = course.c_id AND course.c_name = '数据库原理');
(10) SELECT student.s_id, student.s_name, student.department, course.c_id, course.c_name, score.score FROM student, score, course WHERE student.s_id = score.s_id(+) AND score.c_id = course.c_id(+);
(11) SELECT student.s_name, score.score FROM student, score, course WHERE student.s_id = score.s_id(+) AND score.c_id = course.c_id(+) AND course.c_name = '数据库';
(12) SELECT s_name AS name, '学生' AS type FROM student UNION SELECT t_name AS name, '老师' AS type FROM teacher;
(13) SELECT course.c_name AS course, indirect_course.c_name AS indirect_course FROM course, indirect_course WHERE course.c_id = indirect_course.c_id(+);
(14) SELECT student.s_id, student.s_name, student.department FROM student WHERE student.s_id NOT IN (SELECT s_id FROM score WHERE c_id = 2);