CODEWITHSUNDEEP
mysqlsqldatabaseinner-join
Vimzy
Vimzy

Reputation: 1975

MySQL Query with Inner Joins Returning Empty Set

This has really been bugging me for a while. I'm trying to write an SQL query to return all courses (names), their instructors (names),and their prerequisite course (if they exist). But my query just isn't working and I don't know what to do anymore. I keep getting an empty set returned.

SELECT course, instructors.inst, 
something 
FROM courses a inner join instructors ON a.course_id = instructors.inst_id
INNER JOIN courses b ON a.prereq = b.course_id where a.prereq IS NOT NULL;

Am I doing something wrong with the multiple inner joins? Any help would be greatly appreciated.

Upvotes: 0

Views: 2461

Answers (2)

S I
S I

Reputation: 80

Try this

SELECT a.course_name AS "Course", instructors.inst_name AS "Instructor", 
b.course_name AS "Prereq"
FROM courses a
LEFT OUTER JOIN instructors ON a.course_id = instructors.inst_id
LEFT OUTER JOIN courses b ON a.prereq = b.course_id

Upvotes: 1

Brijesh pant
Brijesh pant

Reputation: 208

LEFT OUTER JOIN should give You the result.Inner join will return results only in case you have data in all of the joined tables.

Upvotes: 1

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