INNER JOIN查询三个表

Question

I have a three table setup in my database: members, clases, classregistration. The class registration table has m_id and c_id columns that store the member id and class id. For example if the same member registers with more classes it will be rows of same m_id with different c_id. I am trying to view all members that are with a particular class and I have this query but it doesn't return anything. Any suggestions what is wrong in my query? Thanks

SELECT members.member_first_name, classregistration.c_id 
FROM classregistration INNER JOIN clases
ON classregistration.c_id = clases.class_id
WHERE classregistration.c_id = 1

Answer 1

You can give this a try:

SELECT m.member_first_name, cr.c_id 
FROM classregistration cr
  INNER JOIN clases c ON cr.c_id = c.class_id
  INNER JOIN members m ON m.member_id = cr.m_id
WHERE cr.c_id = 1