Mysql : 2 table Join

Question

student_courses (id/student_id/course_id) 및 student_questionnaires (id/student_id/course_id/details) 테이블이 2 개 있습니다. 기본적으로 student_courses 테이블을 실행하고 (student_courses 테이블에서) 코스에 등록한 사람의 목록을 반환하지만 설문지를 작성하지 않았습니다 (student_questionnaires에 항목이 없습니다). 나는 다음 시도했다 : 나는 참여의 유형과 주변 해본 적이

SELECT sc.* FROM student_courses as sc 
LEFT JOIN student_questionnaires as sq on sq.course_id=sc.course_id AND sq.student_id=sc.student_id 

,하지만 난 뭔가를 잘못하고 있어요 생각합니다. sq.course_id IS NULL에 대한

이

Answer 1

봐 :

SELECT sc.* 
FROM 
    student_courses sc 
    LEFT JOIN student_questionnaires sq ON sc.student_id = sq.student_id AND sc.course_id = sq.course_id 
WHERE sq.course_id IS NULL 

Answer 2

SELECT sc.* 
FROM student_courses as sc 
WHERE sc.student_id NOT IN (SELECT student_id FROM student_questionnaires) 

Answer 3

이 시도 :

SELECT DISTINCT Student_ID 
FROM Student_Courses 
WHERE LENGTH(COALESCE(Course_ID)) <> 0 AND Student_ID NOT IN 
    (SELECT student_id Student_Questionnaires) 

의