Question

SELECT subjects.name as name , grades.grade as grade,  concat(instructors.lastname, ", ", instructors.firstname , " ", left(instructors.middlename, 1),".") as instructor
    FROM subjects
    JOIN grades
    JOIN instructors
    WHERE grades.student_id = 1 AND subjects.id = grades.subject_id AND instructors.subject_id = subjects.id

Result is

English    Instructor    Grade
Math       Instructor    Grade

But What I wanted is to give “N/A” in subjects that has no instructors yet. Example

English    Instructor    Grade
Math       Instructor    Grade
Science    N/A           Grade
History    N/A           Grade

How I am going to set a condition in my mySQL so the result will look exactly in the above example?

Thanks In Advance

Answer 1

TRy this ::

USing a left join and a ifnull

SELECT subjects.name as name , grades.grade as grade,  ifnull(concat(instructors.lastname, ", ", instructors.firstname , " ", left(instructors.middlename, 1),"."),'N/A)' as instructor
    FROM subjects
    LEFT JOIN grades on subjects.id = grades.subject_id
    LEFT JOIN instructors on instructors.subject_id = subjects.id
    WHERE grades.student_id = 1