Sql query to join four tables - mysql

Question

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 latest 5 question and answers from my post.if any question without answer is there,it should also display as question details in one row with null answer details.But the above code is getting error.Any help is appreciable.my database is mysql.
tblquest
tblans
result

Answer 1

I think we've finally extracted enough detail to arrive at an 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;
demo here
We left join the answers to the questions, in order to ensure we have keep all questions, including those without answers.
We then left join to the answers again, but this time on a range condition in order to just pick off the most recent answer to the question. If there is no a2 with a date greater than a, then that a must be the most recent answer - this is filtered for by the where a2.ansdate is null clause.
That could also be accomplished with a subquery if you preferred.
Finally, we just order and limit our results in order to get the 5 most recent questions.

Answer 2

Problem with your outer join syntax. Check the comment 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
Refer link for more detail:
Full Outer Join in MySQL
https://dev.mysql.com/doc/refman/5.0/en/outer-join-simplification.html
http://www.w3schools.com/sql/sql_join_full.asp