连接两个表检查一个表的值以显示第二个表的结果

Question

I have these two tables: COURSE and COURSE_SEQUENCE_REPORT

I am trying to display course number, course name, course prerequisite number and course prerequisite name. The prerequisite ID is a is obtained as a relation to the course ID. If the presequisite ID is 11 then the prerequisite name is Mathematics from the course ID. I was able to come up with this:

SELECT C.COURSE_NUMBER AS "COURSE NUMBER", 
C.COURSE_NAME AS "COURSE NAME"
FROM COURSE C JOIN COURSE_SEQUENCE_REPORT CSR
ON CSR.COURSE_ID = C.COURSE_ID
ORDER BY C.COURSE_NUMBER;

...but I am left with the course prerequisite number and name. How do I go about it please? I am confused.

Answer 1

You want two joins:

SELECT C.COURSE_NUMBER AS COURSE_NUMBER, 
       C.COURSE_NAME AS COURSE_NAME,
       CP.COURSE_NUMBER AS PREREQUISITE_NUMBER, 
       CP.COURSE_NAME AS PREREQUISITE_NAME       
FROM COURSE_SEQUENCE_REPORT CSR JOIN
     COURSE C
     ON CSR.COURSE_ID = C.COURSE_ID JOIN
     COURSE CP
     ON CSR.PREREQUISITE_ID = CP.COURSE_ID
ORDER BY C.COURSE_NUMBER;