Tuning Slow Performing Queries - sql-server-2008

Question

I have a query which is taking too long to execute.
I used database tuning advisor to check this query and it suggested some missing indexes and statistics. The problem is I can't create missing index and statistics on those tables because it will slowdown insert/update and affect other scripts. They can't sacrifice their scripts performance because of my query.
Without the help of DTA or disturbing other scripts how do I have to tune my query? Can i break it into small pieces? If so, how?
INSERT INTO #val
SELECT lid.orgid,
lid.periodid,
lid.sourceid,
lid.statementtypecode,
lid.financialsbucketid,
lid.statementcurrencycodeiso,
lid.lineitemid,
lll.financialconceptidglobal,
lid.physicalmeasureid,
CASE
WHEN EXISTS(SELECT TOP 1 '1'
FROM trf.dbo.lineitemfundbdescription LIFD(nolock)
WHERE lll.orgid = lifd.orgid
AND lll.lineitemid = lifd.lineitemid) THEN
(SELECT lifd.lineitemshortdescription
FROM trf.dbo.lineitemfundbdescription LIFD(nolock)
WHERE lll.orgid = lifd.orgid
AND lll.lineitemid = lifd.lineitemid)
ELSE lll.lineitemname
END AS LineItemName,
( CASE
WHEN ( lid.reportedcurrencycodeiso IS NOT NULL
AND fc.iscurrencydependent = 1
AND
lid.statementcurrencycodeiso <> lid.reportedcurrencycodeiso
AND fc.isflowitem = 1 ) THEN
lid.lineiteminstancevalue *
cds.dbo.Exrate(lid.reportedcurrencycodeiso, lid.statementcurrencycodeiso, p.periodenddate)
WHEN ( lid.reportedcurrencycodeiso IS NOT NULL
AND fc.iscurrencydependent = 1
AND lid.statementcurrencycodeiso <> lid.reportedcurrencycodeiso
AND fc.isflowitem = 0
AND p.periodlengthunitcode = 'M' ) THEN lid.lineiteminstancevalue
*
cds.dbo.Getaveragefxrate(lid.reportedcurrencycodeiso, lid.statementcurrencycodeiso,
Dateadd("MONTH", -p.periodlength, p.periodenddate), p.periodenddate)
WHEN ( lid.reportedcurrencycodeiso IS NOT NULL
AND fc.iscurrencydependent = 1
AND lid.statementcurrencycodeiso <> lid.reportedcurrencycodeiso
AND fc.isflowitem = 0
AND p.periodlengthunitcode = 'W' ) THEN lid.lineiteminstancevalue
*
cds.dbo.Getaveragefxrate(lid.reportedcurrencycodeiso, lid.statementcurrencycodeiso,
Dateadd("WEEK", -p.periodlength, p.periodenddate), p.periodenddate)
ELSE lid.lineiteminstancevalue
END ) AS LineItemInstanceValue,
( CASE
WHEN ( lid.reportedcurrencycodeiso IS NOT NULL
AND fc.iscurrencydependent = 1
AND lid.statementcurrencycodeiso <> lid.reportedcurrencycodeiso
AND fc.isflowitem = 1 ) THEN
lid.adjustedforcorporateactionvalue *
cds.dbo.Exrate(lid.reportedcurrencycodeiso, lid.statementcurrencycodeiso, p.periodenddate)
WHEN ( lid.reportedcurrencycodeiso IS NOT NULL
AND fc.iscurrencydependent = 1
AND lid.statementcurrencycodeiso <> lid.reportedcurrencycodeiso
AND fc.isflowitem = 0
AND p.periodlengthunitcode = 'M' ) THEN
lid.adjustedforcorporateactionvalue
*
cds.dbo.Getaveragefxrate(lid.reportedcurrencycodeiso, lid.statementcurrencycodeiso,
Dateadd("MONTH", -p.periodlength, p.periodenddate), p.periodenddate)
WHEN ( lid.reportedcurrencycodeiso IS NOT NULL
AND fc.iscurrencydependent = 1
AND lid.statementcurrencycodeiso <> lid.reportedcurrencycodeiso
AND fc.isflowitem = 0
AND p.periodlengthunitcode = 'W' ) THEN
lid.adjustedforcorporateactionvalue
*
cds.dbo.Getaveragefxrate(lid.reportedcurrencycodeiso, lid.statementcurrencycodeiso,
Dateadd("WEEK", -p.periodlength, p.periodenddate), p.periodenddate)
ELSE lid.adjustedforcorporateactionvalue
END ) AS AdjustedForCorporateActionValue,
lid.reportedcurrencycodeiso,
lid.xbrlelementid,
xbrlele.xbrlelementname,
Cast(NULL AS CHAR(3)),
Cast(NULL AS DATETIME),
Cast(NULL AS DATETIME),
Cast(NULL AS CHAR(1)),
Cast(NULL AS DATETIME),
Cast(NULL AS SMALLINT),
src.dcn,
src.docformat,
lid.asreporteditemid,
ari.docbyteoffset,
ari.docbytelength,
ari.bookmark,
ari.itemdisplayednegativeflag,
ari.itemscalingfactor,
ari.itemdisplayedvalue,
ari.reportedvalue,
ari.reporteddescription,
ari.editeddescription,
src.documentid,
lid.isderived,
lid.statementsectioncode,
IsMissMatchPhysicalMeasureID =0,
lid.istotal,
lid.isexcludedfromstandardization,
si.isdetailed AS IsDetailedSection,
si.ispreliminary AS IsPreliminary,
IsCreditSection =Cast(NULL AS BIT),
IsCreditFCC =Cast(NULL AS BIT),
si.isproforma,
lll.instrumentndaid,
InterimTypeID = CASE p.periodicitycode
WHEN 'A' THEN 0
WHEN 'S' THEN 2
WHEN 'T' THEN 3
WHEN 'Q' THEN 4
END,
si.isnotcomparabletopriorperiod,
si.isfundbspecial,
si.isderived AS IsDerivedSI,
lid.systemderivedtypecode
--FBLog.tasktypeid,
--FBLog.systemstartdatetime,
--FBLog.issplit
FROM trf.dbo.lineiteminstance LID(nolock)
--INNER JOIN #fundbbackwardlog FBLog
-- ON FBLog.orgid = lid.orgid
-- AND FBLog.periodid = lid.periodid
-- AND FBLog.sourceid = lid.sourceid
-- AND FBLog.statementtypecode = lid.statementtypecode
-- AND FBLog.financialsbucketid = lid.financialsbucketid
-- AND FBLog.statementcurrencycodeiso =
-- lid.statementcurrencycodeiso
-- AND lid.asreporteditemid IS NOT NULL
-- AND lid.lineiteminstanceasreporteditemid IS NULL
INNER JOIN trf.dbo.statementinstance SI(nolock)
ON lid.orgid = si.orgid
AND lid.periodid = si.periodid
AND lid.sourceid = si.sourceid
AND lid.statementtypecode = si.statementtypecode
AND lid.financialsbucketid = si.financialsbucketid
AND lid.statementcurrencycodeiso = si.statementcurrencycodeiso
INNER JOIN trf.dbo.period P(nolock)
ON lid.orgid = p.orgid
AND lid.periodid = p.periodid
INNER JOIN trf.dbo.lineitem LLL(nolock)
ON lll.orgid = lid.orgid
AND lll.lineitemid = lid.lineitemid
INNER JOIN trf.dbo.financialconcept FC(nolock)
ON lll.financialconceptidglobal = fc.financialconceptid
LEFT OUTER JOIN trf.dbo.xbrlelement XBRLEle(nolock)
ON lid.xbrlelementid = xbrlele.xbrlelementid
INNER JOIN trf.dbo.asreportedinstance ARI(nolock)
ON lid.orgid = ari.orgid
AND lid.sourceid = ari.sourceid
AND lid.asreporteditemid = ari.asreporteditemid
INNER JOIN trf.dbo.[source] SRC(nolock)
ON src.orgid = ari.orgid
AND src.sourceid = ari.sourceid
WHERE ari.reportedvalue IS NOT NULL --AND SRC.DCN > '' --AND SRC.DocFormat > '' --AND ARI.BookMark > ''

Answer 1

Try to remove functions called in the query like : Exrate() and Getaveragefxrate().
Also change the case statement, where you are using subquery as following.
In the end of the query, use
left outer join trf.lineitemfundbdescription lifd
on lll.orgid = lifd.orgid and lll.lineitemid = lifd.lineitemid
and then the case will be changed to
case
when lifd.orgid is null then lll.lineitemname
else lifd.lineitemshortdescription End As LineItemName
It will fine tune your query to a level and gives you a correct execution plan and advice accordingly.
Remember that execution plan does not show the plan of user defined functions called with in the query.