Oracle query running too slow (approximately taking 5 hrs) - sql

Question

SELECT t1.member_id ,
SUM(t1.paid_amt) AS paid_amt
FROM
(SELECT DISTINCT fm.member_id,
fc.claim_skey_no,
fc.claim_id,
fc.claim_line_no ,
CASE
WHEN fc.claim_type_cd = 'RX'
THEN NVL(fc.rx_paid_amt,0) -- For RX claims use rx_paid_amt as paid amount
ELSE NVL(fc.approved_amt,0)
END AS paid_amt -- For all other claims use approved_amt
,
CASE
WHEN fc.claim_type_cd = 'RX'
THEN fc.submit_dt --For RX claims use submit_dt as paid date
ELSE NVL(fc.paid_dt,NVL(fc.edi_eob_dt,NVL(fc.eob_run_dt,fc.outsource_vndr_paid_dt)))
END AS paid_dt --For all other claims use paid_dt
FROM dwprod.fct_claim fc ,
dwprod.fct_member fm
WHERE fc.mbr_skey_no = fm.member_skey_no
-- The service_from_dt on the claim must be between the reimbursement time period.
AND fc.service_from_dt BETWEEN '31-MAY-2013' AND '30-Jun-2014'
-- The follwong 2 conditions make sure that the calims selected are final-status (unadjusted)
-- For non-RX claims, the adjust_type_cd must be Null and the dw_backout_tag must be Null or 'N'
-- For RX claims only the dw_backout_tag must be Null or 'N', the adjust_type_cd is ignored
AND
CASE
WHEN fc.claim_type_cd = 'RX'
THEN 1
WHEN fc.claim_type_cd <> 'RX'
AND fc.adjust_type_cd IS NULL
THEN 1
ELSE 0
END = 1
AND NVL(fc.dw_backout_tag,'N') = 'N'
-- The claim must be in an 'Approved' status, indicated by a status_type_cd = 'A'
AND fc.status_type_cd = 'A'
-- QNXT claims must be in a 'PAID' status
-- Non QNXT claims in the warehouse are assumed to be paid - There are no pended RX claims.
AND
CASE
WHEN fc.dw_source_cd <> 'QNXT'
THEN 1
WHEN fc.dw_source_cd = 'QNXT'
AND fc.last_status_nm = 'PAID'
THEN 1
ELSE 0
END = 1
-- Dental claims are excluded
AND fc.dw_source_cd <> 'DBP'
-- Excludes any Medicare Non-RCI claims
AND
CASE
WHEN NVL(fc.program_nm,'OTHER') = 'MEDICAID'
AND NVL(fc.enroll_ratecode,'RCI') IN ('RCII','RCV','RCVII')
THEN 0
ELSE 1
END = 0
-- It Fits! claims are excluded
AND NVL(fc.expense_cat_nm,'Other') <> 'FITNESS'
AND NVL(fc.proc1_skey_no,12345) NOT IN (21586,21588,21589)
--
AND
CASE
WHEN NVL(fc.program_nm,'OTHER') = 'MEDICAID'
AND NVL(fc.enroll_ratecode,'RCI') IN ('RCII','RCV','RCVII')
THEN 1
WHEN EXISTS
(SELECT 1
FROM dwprod.fct_member_enroll me
WHERE fm.member_skey_no = me.mbr_skey_no
AND fc.service_from_dt BETWEEN me.segment_effect_dt AND me.segment_term_dt
AND me.program_nm = 'MEDICAID'
AND me.enroll_ratecode IN ('RCII','RCV','RCVII')
)
THEN 1
ELSE 0
END = 1
) t1
--Where t1.paid_dt < '31-JAN-2014'
GROUP BY t1.member_id
HAVING SUM(t1.paid_amt) > 175000

Answer 1

Run an explain plan to see what's causing the slowdown. From the top of my head, this is what's 'killing' you:
WHEN EXISTS
(SELECT 1
FROM dwprod.fct_member_enroll me
WHERE fm.member_skey_no = me.mbr_skey_no
AND fc.service_from_dt BETWEEN me.segment_effect_dt AND me.segment_term_dt
AND me.program_nm = 'MEDICAID'
AND me.enroll_ratecode IN ('RCII','RCV','RCVII')
)
See if you can somehow change this exists logic to something with better performance. The explain plan is a must though!

Answer 2

I'm gonna make a semi-blind guess here, based on similar queries in the DW I'm working with.
Oracle's optimizer gets easily confused by predicates such as:
where (case when ... then ... else ... end) = 1;
The reason is that Oracle grossly over estimate the selectivity.
Check the explain plan like others have said. If you find that the estimated cardinality of table dwprod.fct_claim seems way too low, try unrolling the case statements.
For example, instead of:
AND CASE WHEN fc.dw_source_cd <> 'QNXT' THEN 1
WHEN fc.dw_source_cd = 'QNXT' AND fc.last_status_nm = 'PAID' THEN 1
ELSE 0
END = 1
Write:
and ( fc.dw_source_cd <> 'QNXT'
or (fc.dw_source_cd = 'QNXT' and fc.last_status_nm = 'PAID')
)
Final note. This seems to be less of a problem in version 11, but I have not yet had time to investigate why.

Answer 3

FROM dwprod.fct_claim fc ,
dwprod.fct_member fm
WHERE fc.mbr_skey_no = fm.member_skey_no
This cross join is effectively an inner join. I can't say whether Oracle will optimize this, but there's no reason not to make its job easier:
FROM dwprod.fct_claim fc ,
INNER JOIN dwprod.fct_member fm
ON fc.mbr_skey_no = fm.member_skey_no