Most Efficient Version of PLSQL Stored Procedure - stored-procedures

Question

I am writing a PL/SQL stored procedure which will be called from within a .NET application.
My stored procedure must return
the count of values in a table of part revisions, based on an input part number,
the name of the lowest revision level currently captured in this table for the input part number
the name of the revision level for a particular unit in the database associated with this part number and an input unit ID.
The unit's revision level name is captured within a separate table with no direct relationship to the part revision table.
Relevant data structure:
Table Part has columns:
Part_ID int PK
Part_Number varchar2(30)
Table Part_Revisions:
Revision_ID int PK
Revision_Name varchar2(100)
Revision_Level int
Part_ID int FK
Table Unit:
Unit_ID int PK
Part_ID int FK
Table Unit_Revision:
Unit_ID int PK
Revision_Name varchar2(100)
With that said, what is the most efficient way for me to query these three data elements into a ref cursor for output? I am considering the following option 1:
OPEN cursor o_Return_Cursor FOR
SELECT (SELECT COUNT (*)
FROM Part_Revisions pr
inner join PART pa on pa.part_id = pr.part_id
WHERE PA.PART_NO = :1 )
AS "Cnt_PN_Revisions",
(select pr1.Revision_Name from Part_Revisions pr1
inner join PART pa1 on pa1.part_id = pr1.part_id
WHERE PA.PART_NO = :1 and pr1.Revision_Level = 0)
AS "Input_Revison_Level",
(select ur.Revision_Name from Unit_Revision ur
WHERE ur.Unit_ID = :2) as "Unit_Revision"
FROM DUAL;
However, Toad's Explain Plan returns Cost:2 Cardinality: 1, which I suspect is due to me using DUAL in my main query. Comparing that to option 2:
select pr.Revision_Name, (select count(*)
from Part_Revisions pr1
where pr1.part_id = pr.part_id) as "Count",
(select ur.Revision_Name
from Unit_Revision ur
where ur.Unit_ID = :2) as "Unit_Revision"
from Part_Revisions pr
inner join PART pa on pa.part_id = pr.part_id
WHERE PA.PART_NO = :1 and pr.Revision_Level = 0
Essentially I don't really know how to compare the results from my execution plans, to chose the best design. I have also considered a version of option 1, where instead of joining twice to the Part table, I select the Part_ID into a local variable, and simply query the Part_Revisions table based on that value. However, this is not something I can use the Explain Plan to analyze.

Answer 1

Your description and select statements look different... I based the procedure on the SQL statements.
PROCEDURE the_proc
(
part_no_in IN NUMBER
, revision_level_in IN NUMBER
, unit_id_in IN NUMBER
, part_rev_count_out OUT NUMBER
, part_rev_name_out OUT VARCHAR2
, unit_rev_name_out OUT VARCHAR2
)
AS
BEGIN
SELECT COUNT(*)
INTO part_rev_count_out
FROM part pa
WHERE pa.part_no = part_no_in
AND EXISTS
(
SELECT 1
FROM part_revisions pr
WHERE pa.part_id = pr.part_id
);
SELECT pr1.revision_name
INTO part_rev_name_out
FROM part_revisions pr1
WHERE pr1.revision_level = revision_level_in
AND EXISTS
(
SELECT 1
FROM part pa1
WHERE pa1.part_id = pr1.part_id
AND pa.part_no = part_no_in
);
SELECT ur.revision_name
INTO unit_rev_name_out
FROM unit_revision ur
WHERE ur.unit_id = unit_id_in;
END the_proc;

Answer 2

It looks like you are obtaining scalar values. Rather than return a cursor, just return the values using clean sql statements. I have done this numerous times from .net, it works fine.
Procedure get_part_info(p_partnum in part.part_number%type
, ret_count out integer
, ret_revision_level out part_revisions.revision_level%type
, ret_revision_name out part_revisions.revision_name%type) as
begin
select count(*) into ret_count from ....;
select min(revision_level) into ret_revision_level from ...;
select revision_name in ret_revision_name...;
return;
end;