First consider a query that computes which rows are actually relevant from tablethree
. With the assumption that with "most recently entered result" you mean "most recent enddate
" the following query would gather the appropriate rows:
SELECT sid, MAX(enddate) FROM `tablethree` GROUP BY sid
Now you can build a join to retrieve not only sid
, but all of the data of tablethree
:
SELECT a.*
FROM tablethree a
INNER JOIN (
SELECT sid, MAX(enddate) FROM `tablethree` GROUP BY sid
) b
ON a.sid = b.sid AND a.enddate = b.enddate
This is the result set you actually want to "left join in". You have to insert this into your original query:
SELECT t1.*
FROM tableone AS t1
INNER JOIN tabletwo AS t2
ON t1.cid = t2.id
LEFT OUTER JOIN (
SELECT a.*
FROM tablethree a
INNER JOIN (
SELECT sid, MAX(enddate) FROM `tablethree` GROUP BY sid
) b
ON a.sid = b.sid AND a.enddate = b.enddate
) AS t3
ON t3.sid = t2.sid
WHERE t1.fieldone = 1
AND t1.odate NOT BETWEEN t3.startdate AND t3.enddate
What should also work is the following:
SELECT t1.*
FROM tableone AS t1
INNER JOIN tabletwo AS t2
ON t1.cid = t2.id
LEFT OUTER JOIN tablethree AS t3
ON t3.sid = t2.sid
LEFT OUTER JOIN (
SELECT sid, MAX(enddate) FROM `tablethree` GROUP BY sid
) mostrecent
ON t3.sid = mostrecent.sid AND t3.enddate = mostrecent.enddate
WHERE t1.fieldone = 1
AND t1.odate NOT BETWEEN t3.startdate AND t3.enddate
AND mostrecent.enddate IS NULL
This includes both tablethree
and the new SELECT
as left joins, and sorts out the rows where mostrecent.enddate IS NULL
(meaning those rows which are actually not most recent). This should lead to the same result, but MySQL may be able to compute this result a little faster. EXPLAIN
on both queries should reveal possible differences in computation.
Perhaps you are looking for this:
select issues.id, array_agg(journal.notes) from issues
left outer join journal on (issues.id = journal.issue_id and journal.notes != '')
group by issues.id
Please check this http://sqlfiddle.com/#!1/24db9/2
Best Answer
There is no difference, they are absolutely 100% identical in function - the
OUTER
keyword is optional in the syntax. Personally I preferLEFT OUTER JOIN
as it's a bit more explicit.You can see more details here:
MSDN : Using Outer Joins
and here:
MSDN : FROM (Transact-SQL)
The relevant bit in the latter document:
The same description applies whether you use the
OUTER
keyword or not.