Optimize SQL query sql - sql

Question

I also need help speeding up this query, take 25min on LIVE db, 1 second on TEST db.
This is after some modifications, originally I was querying the db server several hundred times to get the data from a php page using a while loop for each row of the main query, then I tried making a procedure using a temp table to return the data, I canceled the execution after 45min. So then I tried this.
I imagine one could do a inner join on the "select top 1 from NurQueryResults" queries but I couldn't figure it out. I got results but not the most recent at the top, I did an "order by t1.time, t2.time, t3.time...." it did have t1 most recent result at top though, and it returned more results than it should have.
SELECT o.VisitID AS VisitID,
(SELECT TOP 1 Response
FROM NurQueryResults
WHERE QueryID = 'OEDTCAT'
AND VisitID = o.VisitID
ORDER BY DateTime DESC) AS PPN,
(SELECT TOP 1 Response
FROM NurQueryResults
WHERE QueryID = 'OEDTMEAT'
AND VisitID = o.VisitID
ORDER BY DateTime DESC) AS MEAT,
(SELECT TOP 1 Response
FROM OeOrderQueries
WHERE QueryID = 'OESPMOD'
AND VisitID = o.VisitID
ORDER BY RowUpdateDateTime DESC) AS SPMOD,
(SELECT TOP 1 Response
FROM OeOrderQueries
WHERE QueryID = 'OERT3'
AND VisitID = o.VisitID
ORDER BY RowUpdateDateTime DESC) AS SPMOD2,
(SELECT TOP 1 Response
FROM NurQueryResults
WHERE QueryID = 'OEDTDECUB'
AND VisitID = o.VisitID
ORDER BY DateTime DESC) AS DECUB,
(SELECT TOP 1 Response
FROM NurQueryResults
WHERE QueryID = 'OEALL2'
AND VisitID = o.VisitID
ORDER BY DateTime DESC) AS FOODALL,
o.OrderedProcedureName,
o.OrderDateTime,
a.RoomID,
a.BedID,
a.Name,
a.Sex,
DATEDIFF(year, a.ComputedBirthDateTime, GETDATE()) AS Age
FROM OeOrders o
INNER JOIN AdmVisits a
ON o.VisitID = a.VisitID
AND o.Category = 'DIET'
AND o.StatusChoice = 'S'
AND a.Status = 'ADM IN'
ORDER BY o.VisitID,
o.OrderDateTime DESC

Answer 1

I'm just wondering, how would the results be when you do something like this:
SELECT
o.VisitID AS VisitID,
PPN.Response
FROM OeOrders o
JOIN AdmVisits a
ON o.VisitID = a.VisitID
AND o.Category = 'DIET'
AND o.StatusChoice = 'S'
AND a.Status = 'ADM IN'
join
(
SELECT
Response,
VisitID,
ROW_NUMBER() OVER(ORDER BY DateTime DESC) AS MyRowNumber
FROM NurQueryResults
WHERE QueryID = 'OEDTCAT'
) AS PPN
on o.VisitID = PPN.VisitID
and PPN.MyRowNumber = 1
This is not your entire query, but just the first sub-query which gets column PPN.
If you change all sub-queries like this JOIN, does it have any performance gain?

Answer 2

Turn on the Execution Plan and check out the results. It may show that you are missing an index or something of that nature.
Speaking of indexes check the fragmentation of the indexes involved and if they're high consider rebuilding them. I have had quite a lot of success recently in getting procedures that took 2min to run on production to execute in 1-3 seconds by following the above process.