How can I optimize the SQL query? - sql

Question

I have a query an SQL query as follows, can anybody suggest any optimization for this; I think most of the effort is being done for the Union operation - is there anything else can be done to get the same result ?
Basically I wanna query first portion of the UNION and if for each record there is no result then the second portion need to be run. Please help.
:
SET dateformat dmy;
WITH incidentcategory
AS (
SELECT 1 ord, i.IncidentId, rl.Description Category FROM incident i
JOIN IncidentLikelihood l ON i.IncidentId = l.IncidentId
JOIN IncidentSeverity s ON i.IncidentId = s.IncidentId
JOIN LikelihoodSeverity ls ON l.LikelihoodId = ls.LikelihoodId AND s.SeverityId = ls.SeverityId
JOIN RiskLevel rl ON ls.RiskLevelId = rl.riskLevelId
UNION
SELECT 2 ord, i.incidentid,
rl.description Category
FROM incident i
JOIN incidentreportlikelihood l
ON i.incidentid = l.incidentid
JOIN incidentreportseverity s
ON i.incidentid = s.incidentid
JOIN likelihoodseverity ls
ON l.likelihoodid = ls.likelihoodid
AND s.severityid = ls.severityid
JOIN risklevel rl
ON ls.risklevelid = rl.risklevelid
) ,
ic AS (
SELECT ROW_NUMBER() OVER (PARTITION BY i.IncidentId ORDER BY (CASE WHEN incidentTime IS NULL THEN GETDATE() ELSE incidentTime END) DESC,ord ASC) rn,
i.incidentid,
dbo.Incidentdescription(i.incidentid, '',
'',
'', '')
IncidentDescription,
dbo.Dateconverttimezonecompanyid(closedtime,
i.companyid)
ClosedTime,
incidenttime,
incidentno,
Isnull(c.category, '')
Category,
opencorrectiveactions,
reportcompleted,
Isnull(classificationcompleted, 0)
ClassificationCompleted,
Cast (( CASE
WHEN closedtime IS NULL THEN 0
ELSE 1
END ) AS BIT)
IncidentClosed,
Cast (( CASE
WHEN investigatorfinishedtime IS NULL THEN 0
ELSE 1
END ) AS BIT)
InvestigationFinished,
Cast (( CASE
WHEN investigationcompletetime IS NULL THEN 0
ELSE 1
END ) AS BIT)
InvestigationComplete,
Cast (( CASE
WHEN investigatorassignedtime IS NULL THEN 0
ELSE 1
END ) AS BIT)
InvestigatorAssigned,
Cast (( CASE
WHEN (SELECT Count(*)
FROM incidentinvestigator
WHERE incidentid = i.incidentid
AND personid = 1588
AND tablename = 'AdminLevels') = 0
THEN 0
ELSE 1
END ) AS BIT)
IncidentInvestigator,
(SELECT dbo.Strconcat(osname)
FROM (SELECT TOP 10 osname
FROM incidentlocation l
JOIN organisationstructure o
ON l.locationid = o.osid
WHERE incidentid = i.incidentid
ORDER BY l.locorder) loc)
Location,
Isnull((SELECT TOP 1 teamleader
FROM incidentinvestigator
WHERE personid = 1588
AND tablename = 'AdminLevels'
AND incidentid = i.incidentid), 0)
TeamLeader,
incidentstatus,
incidentstatussearch
FROM incident i
LEFT OUTER JOIN incidentcategory c
ON i.incidentid = c.incidentid
WHERE i.isdeleted = 0
AND i.companyid = 158
AND incidentno <> 0
--AND reportcompleted = 1
--AND investigatorassignedtime IS NOT NULL
--AND investigatorfinishedtime IS NULL
--AND closedtime IS NULL
),
ic2 AS (
SELECT * FROM ic WHERE rn=1
)
SELECT * FROM ic2
--WHERE rownumber >= 0
-- AND rownumber < 0 + 10
--WHERE ic2.incidentid in(53327,53538)
--WHERE ic2.incidentid = 53338
ORDER BY incidentid DESC
Following is the execution plan I got:
https://www.dropbox.com/s/50dcpelr1ag4blp/Execution_Plan.sqlplan?dl=0

Answer 1

There are several issues:
1) use UNION ALL instead of UNION ALL to avoid the additional operation to aggregate the data.
2) try to modify the numerous function calls (e.g. dbo.Incidentdescription() ) to be an in-lie table valued function so you can reference it using CROSS APPLY or OUTER APPLY. Especially, if those functions referencing a table again.
3) move the subqueries from the SELECT part of the query to the FROM part using CROSS APPLY or OUTER APPLY again.
4) after the above is done, check the execution plan again for any missing indexes. Also, run the query with STATISTICS TIME, IO on to verify that the number of times a table
is referenced is correct (sometimes the execution plan put you in the wrong direction, especially if function calls are involved)...

Answer 2

Since the first inner query produces rows with ord=1 and the second produces rows with ord=2, you should use UNION ALL instead of UNION. UNION will filter out equal rows and since you will never get equal rows it is more efficient to use UNION ALL.
Also, rewrite your query to not use the WITH construct. I've had very bad experiences with this. Just use regular derived tables instead. In the case the query is still abnormally slow, try to serialize some derived tables to a temporary table and query the temporary table instead.

Answer 3

Try alternate approach by removing
(SELECT dbo.Strconcat(osname)
FROM (SELECT TOP 10 osname
FROM incidentlocation l
JOIN organisationstructure o
ON l.locationid = o.osid
WHERE incidentid = i.incidentid
ORDER BY l.locorder) loc)
Location,
Isnull((SELECT TOP 1 teamleader
FROM incidentinvestigator
WHERE personid = 1588
AND tablename = 'AdminLevels'
AND incidentid = i.incidentid), 0)
TeamLeader
from the SELECT. Avoid using complex functions/sub-queries in select.