Optimizing query

Question

SELECT
XREF.MEDICAID_NO,
XREF.PLAN_CODE,
XREF.REVENUE_YEAR,
XREF.REVENUE_MONTH
FROM
table1 a,
table2 b
WHERE
(a.MEDICAID_NO = b.MEDICAID_NO
OR a.EMPLOYEE_NO=b.EMPLOYEE_NO)
AND COMPANY_CODE = 'ACMD'
MINUS
SELECT
A.MEDICAID_NO,
A.PLAN_CODE,
A.REVENUE_YEAR,
A.REVENUE_MONTH
FROM
table1 a,
table2 b
WHERE
TO_CHAR (A.REVENUE_YEAR || LPAD(A.REVENUE_MONTH,2,0)) >= TO_CHAR (B.EFFECTIVE_DATE,'YYYYMM')
AND (B.TERM_DATE IS NULL OR TO_CHAR (A.REVENUE_YEAR || LPAD(A.REVENUE_MONTH,2,0)) <= TO_CHAR (B.TERM_DATE,'YYYYMM'))
AND A.PLAN_CODE = B.PLAN_CODE
AND (A.MEDICAID_NO = B.MEDICAID_NO
OR A.EMPLOYEE_NO=B.EMPLOYEE_NO)
AND A.COMPANY_CODE = 'ACMD';
no of record table1=400000
table2=300000
Basically it takes long time to run this query can you please suggest some ways so that time taken can be reduced to some extent.

Answer 1

As per your idea there are no indexes on revenue_year,revenue_month as such.
Datatypes of the column are varchar2 and date datatypes.
00:05:31.07
0 SELECT STATEMENT Optimizer=CHOOSE (Cost=48357 Card=494339 By
tes=24717016)
1 0 MINUS
2 1 SORT (UNIQUE) (Cost=38413 Card=494336 Bytes=24716800)
3 2 CONCATENATION
4 3 MERGE JOIN (Cost=9043 Card=5497 Bytes=274850)
5 4 SORT (JOIN) (Cost=983 Card=65556 Bytes=1180008)
6 5 TABLE ACCESS (FULL) OF 'MRR_INVOICE_ELIG_TEMP' (
Cost=218 Card=65556 Bytes=1180008)
7 4 SORT (JOIN) (Cost=8060 Card=243521 Bytes=7792672)
8 7 TABLE ACCESS (FULL) OF 'MRR_PAYMENT_INVOICE_XREF
' (Cost=1884 Card=243521 Bytes=7792672)
9 3 MERGE JOIN (Cost=9043 Card=5497 Bytes=274850)
10 9 SORT (JOIN) (Cost=983 Card=65556 Bytes=1180008)
11 10 TABLE ACCESS (FULL) OF 'MRR_INVOICE_ELIG_TEMP' (
Cost=218 Card=65556 Bytes=1180008)
12 9 FILTER
13 12 SORT (JOIN)
14 13 TABLE ACCESS (FULL) OF 'MRR_PAYMENT_INVOICE_XR
EF' (Cost=1884 Card=243521 Bytes=7792672)
15 1 SORT (UNIQUE) (Cost=9944 Card=3 Bytes=216)
16 15 MERGE JOIN (Cost=9943 Card=3 Bytes=216)
17 16 SORT (JOIN) (Cost=1883 Card=65556 Bytes=2622240)
18 17 TABLE ACCESS (FULL) OF 'MRR_INVOICE_ELIG_TEMP' (Co
st=218 Card=65556 Bytes=2622240)
19 16 FILTER
20 19 SORT (JOIN)
21 20 TABLE ACCESS (FULL) OF 'MRR_PAYMENT_INVOICE_XREF
' (Cost=1884 Card=243521 Bytes=7792672)
what can be done next??
Kindly suggest some solutions