Use of NVL, Is it correct or wrong

Question

Hi,
I've doubt regarding the use of NVL in SQL query,
Eg.
for query :
SELECT *
FROM NBS_POLICY_MST
WHERE ORG_POLICY_ID = NVL(:p1,ORG_POLICY_ID);
PLAN_TABLE_OUTPUT
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)|
| 0 | SELECT STATEMENT | | 2084 | 439K| 33 (4)|
| 1 | CONCATENATION | | | | |
| 2 | FILTER | | | | |
| 3 | TABLE ACCESS FULL | NBS_POLICY_MST | 2083 | 439K| 30 (4)|
| 4 | FILTER | | | | |
| 5 | TABLE ACCESS BY INDEX ROWID| NBS_POLICY_MST | 1 | 216 | 3 (0)|
| 6 | INDEX RANGE SCAN | IDXPT_NMP_TRAIL | 1 | | 2 (0)|
In above plan there is an FTS
but if I convert the query to
SELECT *
FROM NBS_POLICY_MST
WHERE POLICY_ID = :p1 or :p1 is null;
PLAN_TABLE_OUTPUT
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)|
| 0 | SELECT STATEMENT | | 105 | 22680 | 29 (0)|
| 1 | TABLE ACCESS FULL| NBS_POLICY_MST | 105 | 22680 | 29 (0)|
the plan table output cost decreased little.
Can anyone help me in the above query which one is the best practice and why and
for the other one why it is consuming more memory
If possible provide a comprehensive description for my above doubt,
thanks in advance
regards/ goutam

Answer 1

SELECT  *
FROM    NBS_POLICY_MST
WHERE   ORG_POLICY_ID   = NVL(:p1,ORG_POLICY_ID);
PLAN_TABLE_OUTPUT
| Id  | Operation                     | Name            | Rows  | Bytes | Cost (%CPU)|
|   0 | SELECT STATEMENT              |                 |  2084 |   439K|    33   (4)|
|   1 |  CONCATENATION                |                 |       |       |            |
|   2 |   FILTER                      |                 |       |       |            |
|   3 |    TABLE ACCESS FULL          | NBS_POLICY_MST  |  2083 |   439K|    30   (4)|
|   4 |   FILTER                      |                 |       |       |            |
|   5 |    TABLE ACCESS BY INDEX ROWID| NBS_POLICY_MST  |     1 |   216 |     3   (0)|
|   6 |     INDEX RANGE SCAN          | IDXPT_NMP_TRAIL |     1 |       |     2   (0)|
--------------------------------------------------------------------------------------here the problem comes when org_policy_id is a nullable field. what if both org_policy_id is null and : p is null. It will not be matched.
Hence i guess oracle does perdicate like this.
(:p is null and org_policy_id is not null) or (:p is not null and org_policy_id = :p)
SELECT  *
FROM    NBS_POLICY_MST
WHERE   POLICY_ID   = :p1 or :p1 is null;
PLAN_TABLE_OUTPUT
| Id  | Operation         | Name           | Rows  | Bytes | Cost (%CPU)|
|   0 | SELECT STATEMENT  |                |   105 | 22680 |    29   (0)|
|   1 |  TABLE ACCESS FULL| NBS_POLICY_MST |   105 | 22680 |    29   (0)|
-------------------------------------------------------------------------I guess this is the correct way to do it and not NVL.