Execution plan too expensive case when exists - sql

Question

I have the below query, but when I execute it runs forever.
WITH aux AS (
SELECT
contract,
contract_account,
business_partner,
payment_plan,
installation,
contract_status
FROM
reta.mv_integrated_md a
WHERE
contract_status IN (
'LIVE',
'FINAL'
)
), aux1 AS (
SELECT
a.*,
CASE
WHEN EXISTS (
SELECT
NULL
FROM
aux b
WHERE
b.business_partner = a.business_partner
AND b.installation = a.installation
AND b.payment_plan = 'BMW'
) THEN
'X'
END h
FROM
aux a
)
SELECT
*
FROM
aux1;
My execution plan shows a huge cost which I cannot locate. How could I optimize this query? I have tried some hints but none of them have worked :(
Plan hash value: 1662974027
----------------------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | Pstart| Pstop |
----------------------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 19M| 2000M| 825G (1)|999:59:59 | | |
|* 1 | VIEW | | 19M| 990M| 41331 (1)| 00:00:02 | | |
| 2 | TABLE ACCESS STORAGE FULL | SYS_TEMP_0FDA49C92_9A7BE8DE | 19M| 1066M| 41331 (1)| 00:00:02 | | |
| 3 | TEMP TABLE TRANSFORMATION | | | | | | | |
| 4 | LOAD AS SELECT | SYS_TEMP_0FDA49C92_9A7BE8DE | | | | | | |
| 5 | PARTITION RANGE SINGLE | | 18M| 974M| 759K (1)| 00:00:30 | 1 | 1 |
|* 6 | TABLE ACCESS STORAGE FULL| MV_INTEGRATED_MD | 18M| 974M| 759K (1)| 00:00:30 | 1 | 1 |
| 7 | VIEW | | 19M| 2000M| 41331 (1)| 00:00:02 | | |
| 8 | TABLE ACCESS STORAGE FULL | SYS_TEMP_0FDA49C92_9A7BE8DE | 19M| 1066M| 41331 (1)| 00:00:02 | | |
----------------------------------------------------------------------------------------------------------------------------
Kindly let me know if any additional information needed.

Answer 1

Use window functions:
SELECT r.contract, r.contract_account, r.business_partner,
r.payment_plan, r.installation, r.contract_status,
MAX(CASE WHEN r.payment_plan = 'BMW' THEN 'X' END) OVER (PARTITION BY business_partner, installation) as h
FROM reta.mv_integrated_md#rbip r
WHERE r.contract_status IN ('LIVE', 'FINAL');
Not only is the query much simpler to write and read, but it should perform much better too.

Answer 2

Highest cost is due to FTS(Full table scan) on table/MV MV_INTEGRATED_MD.
Try to create index on contract_status and check if it reduces the cost and also, what is size of this mv/table in terms of block and it is 10 percent or more than total buffer cache size ?
TABLE ACCESS STORAGE FULL| MV_INTEGRATED_MD | 18M| 974M| 759K (1)| 00:00:30 | 1 | 1

Answer 3

If you run your query with the /*+ gather_plan_statistics */ hint (I'm simulating it with a 1000 row table) you imediately see the problem :
select * from table(dbms_xplan.display_cursor(null,null,'ALLSTATS LAST'));
-------------------------------------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Starts | E-Rows | A-Rows | A-Time | Buffers | Reads |
-------------------------------------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | | 1000 |00:00:00.01 | 9 | 5 |
|* 1 | VIEW | | 1000 | 1000 | 1000 |00:00:00.09 | 0 | 0 |
| 2 | TABLE ACCESS FULL | SYS_TEMP_0FD9D6737_1A17DE13 | 1000 | 1000 | 500K|00:00:00.08 | 0 | 0 |
| 3 | TEMP TABLE TRANSFORMATION | | 1 | | 1000 |00:00:00.01 | 9 | 5 |
| 4 | LOAD AS SELECT (CURSOR DURATION MEMORY)| SYS_TEMP_0FD9D6737_1A17DE13 | 1 | | 0 |00:00:00.01 | 8 | 5 |
|* 5 | TABLE ACCESS FULL | MV_INTEGRATED_MD | 1 | 1000 | 1000 |00:00:00.01 | 7 | 5 |
| 6 | VIEW | | 1 | 1000 | 1000 |00:00:00.01 | 0 | 0 |
| 7 | TABLE ACCESS FULL | SYS_TEMP_0FD9D6737_1A17DE13 | 1 | 1000 | 1000 |00:00:00.01 | 0 | 0 |
-------------------------------------------------------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter(("B"."BUSINESS_PARTNER"=:B1 AND "B"."INSTALLATION"=:B2 AND "B"."PAYMENT_PLAN"='BMW'))
5 - filter("CONTRACT_STATUS"='LIVE')
It is in the line 2 where a full scan is activated in a loop for each line of the main table (see starts = 1000)
Typically you want to resolve the EXISTS with a semi join to preserve good performance, but here it seems that Oracle can not rewrite it.
So you'll need to rewrite the query yourself.
Despite the excelent proposal of #GordonLinoff (that I'll start with) you may try to use an outer join as follows
with bmw as (
select distinct business_partner, installation
from mv_integrated_md
where payment_plan = 'BMW')
SELECT
a.contract,
a.contract_account,
a.business_partner,
a.payment_plan,
a.installation,
a.contract_status,
case when b.business_partner is not null then 'X' end as h
FROM mv_integrated_md a
left outer join bmw b
on b.business_partner = a.business_partner and
b.installation = a.installation
WHERE a.contract_status IN ( 'LIVE', 'FINAL')
This will lead to two fulls scans, one deduplication and outer join.