Slow TSQL query with nested selects - sql

Question

I have written a query, but appears to run quite slowly in our live environment.
The query contains nested select statements which I believe to slow down execution.
Does anyone have any tips of how I could re-write the query to improve the execution speed.
DECLARE #StartDate DATETIME
DECLARE #EndDate DATETIME
SET #StartDate = '20140101'
SET #EndDate = '20140101'
SELECT a.applicationid,
a.ourreference,
(SELECT MAX(e.CreateDateTime) FROM tblEmail AS e WHERE( e.ApplicationID = a.ApplicationID) AND (ISNULL(e.StandardEmailID,0) <> 3)) AS 'LastEmail',
(SELECT MAX(l.CreateDateTime) FROM tblLetter AS l WHERE l.ApplicationID = a.ApplicationID AND l.ExternalDocumentTypeID IS NULL) AS 'LastInternalLetter',
(SELECT MAX(l.CreateDateTime) FROM tblLetter AS l WHERE l.ApplicationID = a.ApplicationID AND l.ExternalDocumentTypeID IS NOT NULL) AS 'LastExternalLetter'
INTO #Temp
FROM tblapplication AS a
WHERE (a.LogDate BETWEEN #StartDate AND #EndDate + '23:59:59')
AND (a.BusinessSourceID NOT IN (11, 16))
AND (a.ApplicationStatusID = 100)
SELECT *
FROM #Temp AS tem
WHERE ((LastEmail < LastExternalLetter) AND (LastInternalLetter < LastExternalLetter))
Cheers everyone
edit- Sorry I should say what the query is for. I am trying to see if our customers have sent us a letter and we haven't responded to them with a letter/email

Answer 1

select *
from
(
Select a.applicationId, a.ourreference,
max(e.CreateDateTime) LastEmail,
max(li.CreateDateTime) LastInternalLetter,
max(le.CreateDateTime) LastExternalLetter
from tblApplication a
left outer join tblEmail e on e.ApplicationID = a.ApplicationID
left outer join tblLetter li on li.ApplicationId = a.ApplicationId
left outer join tblLetter le on le.ApplicationId = a.ApplicationId
WHERE (a.LogDate BETWEEN #StartDate AND #EndDate + '23:59:59')
AND (a.BusinessSourceID NOT IN (11, 16))
AND (a.ApplicationStatusID = 100)
and (e.StandardEmailID <> 3 or e.StandardEmailId is null)
group by a.ApplicationId, a.OurReference
)x
WHERE ((LastEmail < LastExternalLetter) AND (LastInternalLetter < LastExternalLetter))
This gets rid of the temporary table. Remember, with SQL wherever you have a Table you can substitute a query (in Selects anyway). This should make it a bit more efficient, but you want to look at the Query Plans and see what's holding it up.
Cheers -