Mysql 如何将一个SQL表中的两列连接到另一个SQL表中的一列？

我正在使用MYSQL。我的数据库中有两个表

表1：“courseTable”有两个列：

courseId
courseName

courseId
prereqCourseId

表2：“prereqTable”有两个列：

courseId
courseName

courseId
prereqCourseId

表2中的两列都对应于表1中的courseId。我正在尝试运行一个查询，该查询将生成一个包含courseId的courseName和prereqCourseId的courseName的表

我被困在这里：

SELECT `course`.courseName, `prereq`.prereqCourseId FROM `course`
LEFT OUTER JOIN `prereq`
ON `course`.courseId = `prereq`.courseId

---

可以两次连接同一个表，只需为每个实例中的表指定不同的别名，以便从表的相应实例中选择列。像这样：

SELECT
    `course_main`.courseName,
    `course_prereq`.courseName AS `prereqCourseName`

FROM `course` AS `course_main`

LEFT OUTER JOIN `prereq`
ON `course_main`.courseId = `prereq`.courseId

LEFT OUTER JOIN `course` AS `course_prereq`
ON `course_prereq`.courseId = `prereq`.prereqCourseId

---

您需要连接课程表两次，并参考prereqTable

SELECT a.courseName,c.courseName
FROM courseTable AS a
LEFT OUTER JOIN prereqTable AS b ON a.courseId=b.courseId
LEFT OUTER JOIN courseTable AS c ON b.prereqCourseId=c.courseId

---

如果要两次联接同一个表，则必须使用别名

SELECT p.name AS parent, c.name AS child
  FROM relations AS r
  LEFT JOIN nodes AS p
    ON(p.id=r.parent)
  LEFT JOIN nodes AS c
    ON(c.id=r.child )

AS

是可选的，但推荐使用，因为它提高了可读性，并表明您不仅仅忘记了逗号。比较：

SELECT  a b, c d, e, f, g, h i, ...

SELECT a AS b, c AS d, e, f, g, h AS i, ...

---

只需连接到同一个表两次..可能的重复项您需要在第二次连接中使用“prereqCourseId”作为参考，以根据prereqCourseId获取课程名称..感谢您提供更深入的解释