Question

I am using MYSQL. I have two tables in my database.

Table 1: ‘courseTable’ has two colums:

courseId
courseName

Table 2: ‘prereqTable’ has two colums:

courseId
prereqCourseId

Both columns in table 2 correspond to courseId in table 1. I am trying to run a query that will result in a table that contains the courseName for the courseId and the courseName of the prereqCourseId.

I am stuck here:

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

Answer 1

You need to join the course table twice with referecing to prereqTable table

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