Query too slow

Question

Hi All,
I am firing the following query in a view to fetch data.
But the query is taking too much time to execute.
Iam using oracle8i. Please let me know if there are any suggestions on this query.
select MWN_VIEW.* from
select distinct pre.MERCHANT_NAME,pre.SIC_CODE as MCC_CODE,pre.MERCHANT_STATE,exp.AMTTAXUSD,exp.EXPDATE, decode(nvl(exp.AMTTAXUSD,0),0,'N','Y') ReportedTax
from ERSTMP.pre,ERSTMP.CLM,ERSTMP.exp
where
clm.RPTKEY=exp.RPTKEY AND
clm.RPTKEY=pre.RPTKEY AND
exp.PARIND <> 'Y' AND
clm.RPTTYPE = 'PCD'
and pre.PREFILLKEY=exp.PREFILLKEY
) MWN_view,
select min(exp.EXPDATE) Exp_date,pre.MERCHANT_NAME,Merchant_state from ERSTMP.pre,
ERSTMP.exp,ERSTMP.CLM
where
clm.RPTKEY=exp.RPTKEY AND
clm.RPTKEY=pre.RPTKEY AND
exp.PARIND <> 'Y' AND
clm.RPTTYPE = 'PCD'
and pre.PREFILLKEY=exp.PREFILLKEY
group by pre.MERCHANT_NAME,Merchant_state
) MWN_SD_View
where
MWN_View.MERCHANT_NAME=MWN_SD_View.MERCHANT_NAME
and MWN_View.EXPDATE=MWN_SD_View.Exp_date
and MWN_View.MERCHANT_STATE=MWN_SD_View.MERCHANT_STATE
and
MWN_view.MERCHANT_NAME not in
select A1.merchant_name from
select erstmp.pre.merchant_name from erstmp.pre,ERSTMP.CLM,ERSTMP.exp
where clm.RPTKEY=exp.RPTKEY AND
clm.RPTKEY=pre.RPTKEY AND
exp.PARIND <> 'Y' AND
clm.RPTTYPE = 'PCD'
and pre.PREFILLKEY=exp.PREFILLKEY
) A1,
(Select
decode(instr(NVL(Merchantswhochargetax.MERCHANTNAME,' '),'~'),
0, Merchantswhochargetax.MERCHANTNAME,
SUBSTR(Merchantswhochargetax.MERCHANTNAME,1,instr(NVL(Merchantswhochargetax.MERCHANTNAME,' '),'~')-1)) as MERCHANTNAME
from Merchantswhochargetax) A2
where
instr(A1.merchant_name,A2.MERCHANTNAME)>0

Answer 1

Also: how long is it taking to run and how long would you like it to take?
Also: what version of the database are you running?
Also: post some stats. I would guess it's doing some heavy sorts.
Also: it's pretty ugly, lots of the same tables in the sub-queries - is there really no better way of sharing the data? If you're using 9i you really ought to investigate the WITH clause of the SELECT statement.
Finally, why so many in-line views? It makes your query harder to read.
Good luck, APC
SELECT DISTINCT pre.merchant_name
       , pre.sic_code as mcc_code
       , pre.merchant_state
       , exp.amttaxusd
       , exp.expdate
       , decode(nvl(exp.amttaxusd,0),0,'N','Y') reportedtax
FROM   erstmp.pre
       , erstmp.clm
       , erstmp.exp
WHERE  clm.rptkey=exp.rptkey
AND    clm.rptkey=pre.rptkey
AND    exp.parind <> 'Y'
AND    clm.rpttype = 'PCD'
AND    pre.prefillkey=exp.prefillkey
AND    exp.expdate = ( SELECT min(exp1.expdate)
                       FROM   erstmp.pre pre1
                              , erstmp.clm clm1
                              , erstmp.exp exp1
                       WHERE  clm1.rptkey=exp1.rptkey
                       AND    clm1.rptkey=pre1.rptkey
                       AND    exp1.parind <> 'Y'
                       AND    clm1.rpttype = 'PCD'
                       AND    pre1.prefillkey=exp1.prefillkey )
AND    pre.merchant_name NOT IN ( SELECT pre2.merchant_name
                                  FROM   erstmp.pre2
                                         , merchantswhochargetax A2
                                         , erstmp.exp2
                                         , erstmp.clm2
                                  WHERE  clm2.rptkey=exp2.rptkey
                                  AND    clm2.rptkey=pre2.rptkey
                                  AND    exp2.parind <> 'Y'
                                  AND    clm22.rpttype = 'PCD'
                                  AND    pre.prefillkey=exp2.prefillkey
                                  AND    instr(erstmp2.pre.merchant_name, substr(a2.merchantname, 1 , decode(instr(a2.merchantname, '~'), 0, length(a2.merchantname), instr(a2.merchantname, '~'))))>0