MySQL Joining three tables
I am doing a query with three tables, the problem was one table has many occurrences of id of another.
sample data:
users: id
answers:
id:1
user_answer :1
id:1
user_answer :2
id:开发者_运维百科1
user_answer :3
Questions:
id:1
answers :answer description
id:2
answers :answer description
id:3
answers :answer description
How can I get all user information and all answer and its description, I used GROUP by user.id but it only returns only one answer.
I want to return something like this list all of users answer:
Name Q1 Q2
USERNAME ans1,ans2 ans1,ans2 comma separated description of answer here
alt text http://christianruado.comuf.com/images/schema.png
You'd need to use a pivot table
SELECT users.id, users.name,
GROUP_CONCAT(q1.answer SEPARATOR ', ') AS `Q1`,
GROUP_CONCAT(q2.answer SEPARATOR ', ') AS `Q2`,
GROUP_CONCAT(q3.answer SEPARATOR ', ') AS `Q3`
FROM `users` AS users,
LEFT JOIN `answers` AS a1 ON a1.id = users.id
LEFT JOIN `questions` AS q1 ON q2.id = a1.user_answer
LEFT JOIN `answers` AS a2 ON a2.id = users.id
LEFT JOIN `questions` AS q2 ON q2.id = a2.user_answer
LEFT JOIN `answers` AS a3 ON a3.id = users.id
LEFT JOIN `questions` AS q3 ON q3.id = a3.user_answer
WHERE q1.question_id = 1
AND q2.question_id = 2
AND q3.question_id = 3
GROUP BY users.id
That's my best guess at what you want to do from the schema you provided (I doubt it's complete, which is why I guessed at the question_id part. I used LEFT JOIN so that if the user doesn't have an answer for that question, it won't hurt anything. Also, GROUP_CONCAT will automatically combine the field if multiple answers exist. So if there are 2 rows from Q1 for that particular user, it'll combine the two into "ans1, ans2"...
精彩评论