Sql query to join four tables
SELECt
qst_id,qst_title,ans_date,ans_text
FROM
(
SELECT
a.Question_Id as qst_id,a.Question_Title as qst_title,a.Question_Text as qst_text,DATE_FORMAT(a.LastActivity_Date,'%d %b %Y %T') as qst_date,b.UserForum_Image as qst_prof,b.ScreenName as qst_scname
FROM
tblforumquestion a, tblregistration2_2 b
WHERE a.RegistrationId=b.RegistrationId and a.LastActivity_Date between '2014-0-01 00:00:00' and '2015-05-01 00:00:00'
ORDER BY a.LastActivity_Date desc limit 5
outer join
SELECT
DATE_FORMAT(c.Answer_Date,'%d %b %Y %T') as ans_date,c.Answer_Text as ans_text,d.UserForum_Image as ans_prof,d.ScreenName as ans_scname
FROM
tblforumanswer c ,tblregistration2_2 d
where c.Answer_Id in
(
SELECT MAX(Answer_Id)
FROM tblforumanswer
GROUP BY Question_Id
)
and c.RegistrationId=d.RegistrationId
order by c.Answer_Date desc limit 5
)
I am trying to get the last 5 questions and answers from my post. If you have an unanswered question, it should also display as questions on one line with a zero answer. But the above code is getting error. Any help is greatly appreciated. Mysql database.
tblquest tblans Result
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I think we've finally extracted enough detail to get the answer:
select q.qstid, q.qsttext, a.anstext
from tblquest q
left join tblans a
on q.qstid = a.qstid
left join tblans a2
on a.qstid = a2.qstid and a.ansdate < a2.ansdate
where a2.ansdate is null
order by q.qdate desc limit 5;
We answer questions so that we have all the questions, including unanswered ones.
Then we get the answers again left join
, but this time in range mode to simply select the most recent answer to the question. If not a2
with a date greater than a
, then this a
should be the most recent answer - this is filtered according to the suggestion where a2.ansdate is null
.
This can also be accomplished with a subquery if you prefer.
Finally, we just order and limit our results to get the last 5 questions.
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The problem is with your outer join syntax. Check comments and sample data.
SELECT
qst_id,qst_title,ans_date,ans_text
FROM
(
SELECT
a.Question_Id as qst_id,a.Question_Title as qst_title,a.Question_Text as qst_text,DATE_FORMAT(a.LastActivity_Date,'%d %b %Y %T') as qst_date,b.UserForum_Image as qst_prof,b.ScreenName as qst_scname
FROM
tblforumquestion a, tblregistration2_2 b
WHERE a.RegistrationId=b.RegistrationId and a.LastActivity_Date between '2014-0-01 00:00:00' and '2015-05-01 00:00:00'
ORDER BY a.LastActivity_Date desc limit 5
outer join --Error comes here
SELECT
DATE_FORMAT(c.Answer_Date,'%d %b %Y %T') as ans_date,c.Answer_Text as ans_text,d.UserForum_Image as ans_prof,d.ScreenName as ans_scname
FROM
tblforumanswer c ,tblregistration2_2 d
where c.Answer_Id in
(
SELECT MAX(Answer_Id)
FROM tblforumanswer
GROUP BY Question_Id
)
and c.RegistrationId=d.RegistrationId
order by c.Answer_Date desc limit 5
)
--This is example of outer join
SELECT
A.*, B.*
FROM
TableA a outer join TableB b on a.RegistrationId = b.RegistrationId
See link for details:
https://dev.mysql.com/doc/refman/5.0/en/outer-join-simplification.html
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