I have 3 tables:
Subjects:
ID_subject Subject_name
Questions:
ID_question Question ID_subject
Answers
ID_answer Answer ID_question
Is it possible to make a selection where the result will be all the answers from 3rd subject? I tried to make a double JOIN but that did not work, it returned me all the answers.
This should return the results you're looking for:
SELECT a.ID_answer, a.Answer FROM Answers a
JOIN Questions q ON q.ID_question = a.ID_question
JOIN Subjects s ON s.ID_subject = q.ID_subject
WHERE s.ID_subject = ID_of_third_subject
Related
I am working with MYSQL, and want to create a query. I have 3 tables.
QUESTION
QUESTION_NUMBER
QUESTION_DESCRIPTION
1
anydesc
2
anydesc2
ANSWER
ANSWER_NUMBER
ANSWER_DESCRIPTION
1
anydescANS
2
anydesc2ANS
3
anydesc3ANS
And a bridge TABLE
QUESTION_ANSWER
Q_NUM
A_NUM
1
1
2
2
2
3
Now I want to retrieve all the Answers of let's say a specific QUESTION NUMBER i.e 1.
What I have tried.
SELECT QUESTION.QUESTION_NUMBER, QUESTION.QUESTION_DESCRIPTION, ANSWER.ANSWER_NUMBER, ANSWER.ANSWER_DESCRIPTION
FROM QUESTION
RIGHT JOIN QUESTION_ANSWER ON QUESTION.QUESTION_NUMBER=4
INNER JOIN ANSWER ON QUESTION_ANSWER.Q_NUM=4
and similar queries, but I can not make sense of it, and can not get desired output.
What I want is to get all the answers that belong to specific Question Number.
I would write it this way:
SELECT
Q.QUESTION_NUMBER,
Q.QUESTION_DESCRIPTION,
A.ANSWER_NUMBER,
A.ANSWER_DESCRIPTION
FROM QUESTION AS Q
INNER JOIN QUESTION_ANSWER AS QA ON Q.QUESTION_NUMBER = QA.Q_NUM
INNER JOIN ANSWER AS A ON QA.A_NUM = A.ANSWER_NUMBER
WHERE Q.QUESTION_NUMBER=4;
You don't need RIGHT OUTER JOIN, you need INNER JOIN, because there is certain to be a matching question if you are seeking answers.
I recommend avoiding the "comma-style" join syntax. That was made obsolete in 1989. It works the same as inner join, but it's worth using the modern syntax consistently.
This should work for your purpose:
SELECT q.question_number, q.question_description,
a.answer_number, a.answer_description
FROM question q, answer a, question_answer qa
WHERE q.question_number = qa.q_num
AND a.answer_number = qa.a_num
AND q.question_number = 2
MySQL.
I have two tables, one is "Questions" and the other is "Answers"
The Questions table:
- question_id
- user_id
- question
The Answers table:
- answer_id
- question_id
- user_id
- answer
- correct
The goal is to get all questions (and associative answers) based on a user's id. I've been able to get all of the answers, however I'm only getting one question. I can see why it's only getting a single question, but I don't have any idea how to go about getting the question text for each answer.
Here's the code that I'm using right now. Where id_in is an input value on a saved procedure. The issue is that it gives me all of the answers for each question, but all of them return the same question text. I feel like possibly a type of join would be better here, but we haven't started learning about them yet and I hardly know anything about them as is.
BEGIN
DECLARE question_text VARCHAR(40);
SELECT question INTO question_text FROM questions WHERE user_id = id_in;
SELECT question_text, Q.* FROM answers AS Q WHERE user_id = id_in;
END
Yes, this is homework. I'm just completely lost as to what I need to be doing.
Left joins allow for All things in the left table, and only the matching things in the right table. In my example I may have A and Q mixed up but I think this is the general gist of it. You can also take the user_id = in_id and move that to a wear, but filter on the join should be faster.
SELECT
Q.QUESTION
, A.ANSWER
, A.CORRECT
FROM ANSWERS A
LEFT JOIN QUESTION Q
ON A.QUESTION_ID = Q.QUESTION_ID
AND A.USER_ID = Q.USER_ID
AND A.USER_ID = ID_IN
AND Q.USER_ID = ID_IN
MySQLFiddle here: http://sqlfiddle.com/#!2/15d447/1
I have a single table I am trying to work with:
Table 1: user_answers table (stores users answers to various questions)
The notable values that are stored are the users id (column uid), the question id for the question they are answering (column quid), the answer to the question (column answer) and the importance of their answer (column importance).
The end result I want:
I'd like to be able to grab all the questions that any two users have answered, excluding any answers from questions that have either not been answered by the other party, or answers to the same question which have a value of 1 for either user in importance. Again, this will only ever be used to compare two users at a time.
I've been pretty unsuccesful in my attempts, but here is what I've tried, just piecing things together:
#attempt one: trying to exclude answers that were not answered by both users
SELECT * FROM user_answers AS uid1
JOIN user_answers AS uid2 ON uid1.uid = uid2.uid
WHERE uid1.uid = 1
AND uid2.uid = 20008
AND uid1.quid IS NOT NULL
AND uid2.quid IS NOT NULL;
This returns no results but I'm not exactly sure why.
#attempt two: trying to exclude where answers are the same for both users
SELECT * FROM user_answers AS uid1
LEFT JOIN user_answers AS uid2 ON (uid1.uid = uid2.uid AND uid1.answer <> uid2.answer)
This gives me results, but seems to be doubling up on everything because of the join. I also tried in this attempt to eliminate any answers what were the same, which seems to be working in that sense.
Any guidance is appreciated.
Thanks.
You can answer your question using an aggregation query. The idea is to using the having clause to filter the rows for the conditions you are looking at.
Because you are not interested at all in questions with importance = 1 those are filtered using a where clause:
select ua.quid
from user_answers ua
where importance <> 1 and uid in (1, 20008)
group by ua.quid
having sum(uid = 1) > 0 and
sum(uid = 20008) > 0;
If you want to include the answers, you can do:
select ua.quid,
group_concat(concat(uid, ':', answer) order by uid) as answers
Just a simple version of what you need.
select *
from user_answers a,
user_answers b
where a.quid = b.quid
and a.uid <> b.uid
and 1 not in (a.importance, b.importance)
If you like to filter just the questions just change the * for distinct a.quid
See it here on fiddle: http://sqlfiddle.com/#!2/15d447/15
Hi I'm currently developing a sort of quiz application. In "Discover" section I get popular and latest questions. But when I get them I should also check if question is already answered by current user or not.
Here are my tables:
questions: (media_id is primary key, player_id is creator of the question)
media_id - player_id - answer0 - answer1 - ...
answers: (media_id is primary key, player_id is the person who answers the question)
media_id - player_id - result - ...
This is how I get popular questions:
select * from questions where order by popularity_count
EDIT:
Let me show what I want to achieve by examples:
questions rows:
media_id - player_id - answer0 - answer1
0123456 abc123 bla bla
6543210 hjk789 lor ips
answers rows:
media_id - player_id - result
6543210 abc123 1
So when user "abc123" gets the popular questions results should be:
media_id - player_id - answer0 - answer1 - is_answered
0123456 abc123 bla bla 0
6543210 hjk789 lor ips 1
The problem is I need a temporary column in the result of query that indicates if question is replied by the current user or not. How can I achieve this?
I can find if question is already answered or not for popularity section by using two queries. First I get the popular questions then I simply check if question is answered or not for every questions which seems so ineffective way. How can I achieve this with only one query?
Thank you!
It doesn't seem you are approaching this problem correctly as you have a non-normalized table structure.
You should have a separate table that contains the answers by row.
questions (id, media_id, player_id, question)
answers (id, media_id, player_id, question_id, answer)
This way you can LEFT JOIN answers to questions and easily see which questions are not answered like so:
SELECT q.question, a.answer
FROM question q
LEFT JOIN answers a ON a.question_id = q.id
AND a.media_id = q.media_id
AND a.player_id = q.player_id
See it in action
To add a column to your current query, you can append it to your SELECT and use a CASE statement to check whether it's been answered.
SELECT ...,
CASE
WHEN answer0 IS NOT NULL
THEN 'Yes'
ELSE 'No'
END AS 'Answered'
FROM ...
Update
Based on your update, it seems as though you are only JOINing on player_id. I believe you intend to JOIN on both player_id and media_id. See the difference between the data you provided and what I think you intend it to be.
I have Two Table One to store Questions and Other to store Replies to Questions as Below
I have Shown the Table Structure and Column in table as Below
Question Table
Question_Id(PK) | Question | Name | EmailAddress
Answer Table
Answer_Id | Question_Id | Question | Name | EmailAddress
What ever question is posted it will be added to Question table and What ever Replies people post will be added to answer table
Now when ever Some one post a Reply to Question I Should Send mail to one who Posted Question and to those who posted Replies to the Question
Please Suggest a mysql Query for the above
Thank you
In theory you should know in the application the id of the question (qid) someone is replying to. Based on this id you can issue the following query:
Select EmailAddress from Question where Question_Id=qid
Union
Select EmailAddress from answer where Question_id=qid
Depending on the logic of your application this might also select the address of the current user. If you want to avoid this you should include in both select statments a condition to exclude the current replier. Something like:
Select EmailAddress from Question where Question_Id=qid and EmailAddress!=curentUserAddress
Union
Select EmailAddress from answer where Question_id=qid and EmailAddress!=curentUserAddress
Select *
from questions
left join answers
on questions.id = answers.question_id
where question_id = 1
select * from Question q, Answer a
where q.Question_Id = a.Question_id and
q.Question_Id = question_id