Sql-server – SQL join query to show rows with non-existent rows in one table

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.

I splitted the problem into two basic SELECTs, one for members and the another one for guests and I join both later. MySql's GROUP_CONCAT aggregate funtion is very useful here too.

http://sqlfiddle.com/#!9/58786/1

SELECT 
TT1.day as day
,TT1.booking_id as booking_id
,TT1.member_id as member_id
,CASE 
  WHEN TT2.guest_ids IS NULL 
  THEN 0 
  ELSE TT2.guest_ids 
  END as guest_id
,TT1.start_date as start_date
,TT1.end_date as end_date
,CASE 
  WHEN TT2.guest_ids IS NULL
  THEN TT1.member_name
  ELSE CONCAT(TT1.member_name, ', ', TT2.guests_name)
  END as names
FROM
(
SELECT 
Min(day) as day
, booking_id
, member_id
, Members.id
, CONCAT(first_name,' ',last_name) as member_name
, start_date
, end_date   
FROM Bookings
INNER JOIN Members
ON Bookings.member_id = Members.id
WHERE member_id <> 0
GROUP BY booking_id, member_id, guest_id, start_date, end_date
) AS TT1
LEFT JOIN
(
SELECT 
booking_id
, GROUP_CONCAT(guest_id SEPARATOR ', ') as guest_ids
, GROUP_CONCAT(CONCAT(first_name, ' ', last_name) SEPARATOR ', ') as guests_name
FROM
(
SELECT
booking_id
, guest_id
FROM Bookings
WHERE guest_id <> 0
GROUP BY booking_id, guest_id
) AS T1
INNER JOIN Guests
ON T1.guest_id = Guests.id
GROUP BY booking_id
) AS TT2
ON TT1.booking_id = TT2.booking_id
ORDER BY TT1.day, TT1.booking_id