Question

The easiest way to explain this will be to draw out the two tables for you guys – so here it goes..

sl_project_course

project_id   |    course_id
50                    1

sl_course
professor_id |    course_id      | course_name
1                     1                 "history"
1                     2                 "law"
1                     3                 "art"
1                     2                 "law"

Information I already have

• Project_id = 50
• Professor_id = 1

What I want:

I want all of the course_id’s that the professor is teaching, where
the course_id is not affiliated with the project at hand (in this case
the project at hand is 1 – as shown above.

So, the data I want to come back from the query is:

2                 "law"
3                 "art"

** My attempt:**

$sql_course_not_in_project = "SELECT C.course_id, C.course_subject
FROM sl_course C
LEFT OUTER JOIN sl_project_course PC on PC.project_id = 50
WHERE C.course_id <> PC.course_id AND C.professor_id = 1";

This works, except when there are two rows in sl_project_course the query no longer works correctly.

I appreciate any help!

Thanks,

Evan

Answer 1

SELECT c.course_id, c.course_subject
    FROM sl_course c
        LEFT JOIN sl_project_course pc
            ON c.course_id = pc.course_id
                AND pc.project_id = 50
    WHERE c.professor_id = 1
        AND pc.course_id IS NULL