oracle：如何找到符合先决条件的学生

Question

我是甲骨文的新手。如何找到符合先决条件的学生

SELECT
    c.course_no,
    c.description,
    c.prerequisite,
    level AS level_course,
    stu.student_id
FROM
    course c
    INNER JOIN section s ON c.course_no = s.course_no
    INNER JOIN enrollment e ON s.section_id = e.section_id
    INNER JOIN student stu ON e.student_id = stu.student_id
CONNECT BY
    PRIOR c.course_no = c.prerequisite

[1]：https://i.stack.imgur.com/SNG0G.png 课程表

[1]：https://i.stack.imgur.com/Asy8F.png ENROLLMENT TABLE https://i.stack.imgur.com/1axEi.png SECTION TABLE

Answer 1

您可能需要在START WITH之前添加CONNECT BY。

这里以course_no 20为例。

您可以删除AND c.course_no = 20以查看所有课程。

注意：还调整了列以使其更清晰

SELECT
    level AS level_course,
    c.course_no,
    e.section_id,
    c.prerequisite,
    c.description,
    stu.student_id
FROM
    course c
    INNER JOIN section s ON c.course_no = s.course_no
    INNER JOIN enrollment e ON s.section_id = e.section_id
    INNER JOIN student stu ON e.student_id = stu.student_id
START WITH c.prerequisite IS NULL AND c.course_no = 20
CONNECT BY
    PRIOR c.course_no = c.prerequisite