Question

I’m trying to display the information I have in these columns and it keeps telling me that the first_name column in my professors table is unknown. Does anyone know why?
Please help me, I’ve tried everything.
Thanks.

Here’s the query:

SELECT courses.name, sections.section_name, professors.first_name, professors.last_name, classrooms.room
FROM courses
INNER JOIN course_section ON sections.id = course_section.section_id
INNER JOIN professor_course ON professors.id = professor_course.professor_id
WHERE courses.id = 1;

Answer 1

The error is because you haven’t included sections in any from or join. You have the same thing going on with professors.

Personally, I prefer the readability of implied inner joins in this situation. A DBA may disagree, but as a programmer I find this easier to figure out what’s going on.

SELECT courses.name, sections.section_name, professors.first_name, professors.last_name, classrooms.room 
FROM courses, course_section, sections, professors, professor_course, classrooms
WHERE sections.id = course_section.section_id
AND professors.id = professor_course.professor_id 
AND -- classrooms???
AND courses.id = 1; 

Not knowing your DB structure, you can probably get what you are looking for with less table joins.