形成复杂的SQL语句(Forming a complex SQL statement)

 我正忙着为我的一个项目构建一个有效的SQL语句。 首先，我有一个“问题”表和一个“响应”表。 响应表通过名为“question_id”的外部ID（与问题“id”相关联）与问题表相关联。 一个问题不一定得有回应，但我能提出的唯一可行的陈述只会提出一个有回应的问题，但我需要它来表明每个问题是否有回应。 
 
 那个SQL语句是： 
 
SELECT u.firstname, q.question, r.tutor_id, r.response FROM response r 
JOIN question q ON q.id = r.question_id
JOIN user u ON u.id = q.user_id
 
 我的另一个问题是我也试图拉出导师的名字，但只能拉“tutor_id”，所以任何帮助都会很棒。 如果有人有任何提示，我会很感激！ 
 
 适用于： 
 
SELECT u.firstname, q.question, v.firstname, r.response
FROM question q
INNER JOIN user u ON u.id = q.user_di
LEFT JOIN response r ON q.id = r.question_id
LEFT JOIN user v ON v.id = r.tutor_id

I'm coming up stumped on forming a working SQL statement for a project of mine. First of all, I have a "questions" table and a "response" table. The response table is tied to the question table through a foreign id called "question_id" (tied to the questions "id"). A question doesn't necessarily have to have a response, but the only working statement I can come up with will only pull a question that has a response, but I need it to show every question whether or not there is a response.
 
That SQL statement is:
 
SELECT u.firstname, q.question, r.tutor_id, r.response FROM response r 
JOIN question q ON q.id = r.question_id
JOIN user u ON u.id = q.user_id
 
My other problem is that I'm also trying to pull the firstname of the tutor, but can only pull the "tutor_id", so any help with that would also be awesome. If anyone has any tips, I'd appreciate it!
 
Works with:
 
SELECT u.firstname, q.question, v.firstname, r.response
FROM question q
INNER JOIN user u ON u.id = q.user_di
LEFT JOIN response r ON q.id = r.question_id
LEFT JOIN user v ON v.id = r.tutor_id

原文：https://stackoverflow.com/questions/3315130