Oracle 11x Newbie - simple, but sincere... - oracle11g

Question

First, thank you for taking the time to read this, I am fairly well experienced with most versions of MSSQL, but not so much with Oracle and PL SQL.
My problem and question are this:
I have a SSRS report in MSSQK2k12 that is calling a stored proc on an Oracle 11x db. there are several params passed in that are used in the where clause, I need to add one more param ( a simple Y/N) that will add additional filters to the where clause, effectively saying at the report prompt 'do you want to see all parts? (Y/N). A 'Y' answer will run the proc nearly wide open, including parts that have no inventory, parts on hand, but already sold, parts no longer active. A 'N' response will pass filters that require available inventory, valid current part class, etc.
I have attempted a half-dozen seemingly good solutions, to no avail. I have asked an associate (who is well versed in PLSQL) for his advice, his resulting 'DECODE' addition did nothing. I would like to request advice/assistance that does not involve months of study, as I only have a few days to finish. Please note, the original SP was not my work, I have inherited from predecessor would did/could not complete. Stored procedure (Scrubbed) attached
CREATE OR REPLACE PROCEDURE ORACLE_PROD.RPT_LIKE_PARTS_TEST (
p_Pos1 IN varchar2
, p_Description IN varchar2
, p_StartPos IN varchar2
, p_StartPosValue IN varchar2
, p_ViewAll IN varchar2 --ADDED to allow filtered return for data
, p_recordset OUT SYS_REFCURSOR)
AS
BEGIN
OPEN p_recordset FOR
SELECT T1.ITEM
, T1.REVISION
, T1.DESCRIPTION
, T2.CCN
, T2.DELETED
, T2.OBSOLETED
, T2.FINGOOD
, T2.ABC
, T3.MAS_LOC
, T3.LOCATION
, (T3.OH_QTY - T3.COM_QTY) - T3.RESV_QTY as Avail_QTY
, T1.USER_NUM1
, case when T2.HALT<>' ' then 'Y' else NULL end as Halt
, T4.DESCRIPTION as T4_Description
, det.OH_QTY as Det_OH_QTY
, det.COM_QTY as Det_COM_QTY
, DECODE(det.INSP_STAT,'3','Passed Inpection' ,DECODE det.INSP_STAT,'1','Waiting Inspection' ,' ')) as Inspect_Descr
, T3.RESV_QTY
from ITEM T1
LEFT OUTER JOIN ITEM_CCN T2
ON T1.ITEM=T2.ITEM
and T1.REVISION=T2.REVISION
LEFT OUTER JOIN ITEM_LOC T3
on T2.CCN=T3.CCN
and T2.ITEM=T3.ITEM
and T2.REVISION=T3.REVISION
LEFT OUTER JOIN HALT T4
on T2.HALT=T4.HALT
and T2.CCN=T4.CCN
LEFT OUTER JOIN ITEM_DET det
on T3.CCN=det.CCN
and T3.ITEM=det.ITEM
and T3.REVISION=det.REVISION
and T3.MAS_LOC=det.MAS_LOC
and T3.LOCATION=det.LOCATION
where T2.OBSOLETED is null
--** all commented parts are attempted adds
--&&&and CASE (p_ViewAll)
--&&& when 'N'
--&&& THEN --T2.HALT = DECODE(T2.HALT,'DSGN', 'XXX',' ','XXX',T2.HALT)
-- and
--&&& (T2.HALT != 'DSGN' and (((T3.OH_QTY - T3.COM_QTY) - T3.RESV_QTY))> 0
--and T2.HALT <> 'DSGN' and T3.mas_loc <>'99' and T3.mas_loc <>' '
--&&&WHEN 'Y'
--&&& THEN
and T2.HALT <>'DSGN'
--&&&ELSE NULL-- or T3.mas_loc <> '')
--&&&END
--**
/*and T2.HALT = decode(p_ViewAll,'Y',
DECODE(T2.HALT,'DSGN', T2.HALT),
DECODE(T2.HALT,'DSGN', T2.HALT)
--DECODE(T2.HALT,'DSGN', 'XXX',' ','XXX',T2.HALT),
--DECODE(T2.HALT,'DSGN', 'XXX', T2.HALT)
)
and (p_ViewAll != 'Y' or T3.mas_loc not in ('99',' '))*/
--**
AND UPPER(TRIM(T1.ITEM)) LIKE (CASE WHEN LENGTH(TRIM(p_pos1)) > 0 THEN UPPER(TRIM(p_pos1) || '%') ELSE UPPER(TRIM(T1.ITEM))END)
AND UPPER(T1.DESCRIPTION) LIKE (CASE WHEN LENGTH(p_Description) > 0 THEN UPPER(('%' || p_Description || '%')) ELSE UPPER(UPPER(T1.DESCRIPTION))END)
AND
(CASE WHEN TO_NUMBER(NVL(TRIM(p_StartPos),'0')) > 0 THEN SUBSTR(TRIM(T1.ITEM),TO_NUMBER(TRIM(p_StartPos)),NVL(LENGTH(UPPER(TRIM(p_StartPosValue))),'0'))
ELSE 'False'
END)
=
(CASE WHEN TO_NUMBER(NVL(TRIM(p_StartPos),'0')) > 0 THEN NVL(UPPER(TRIM(p_StartPosValue)),'')
ELSE 'False'
END)
ORDER BY T1.ITEM
, T1.revision desc
;
END RPT_LIKE_PARTS_TEST;
/

Answer 1

You have to use UNION and not decode. In one side of UNION you have to handle parameter Y with outer join and other will be as you have coded already.
OR you need to use if / else of PLSQL since user can pass only one of them as parameter.
To be honest, this question is nothing specific to oracle and mere SQL.

Answer 2

so with the union all or union solution probably looks something like this
/* Formatted on 7/5/2016 1:50:34 PM (QP5 v5.256.13226.35510) */
SELECT T1.ITEM,
T1.REVISION,
T1.DESCRIPTION,
T2.CCN,
T2.DELETED,
T2.OBSOLETED,
T2.FINGOOD,
T2.ABC,
T3.MAS_LOC,
T3.LOCATION,
(T3.OH_QTY - T3.COM_QTY) - T3.RESV_QTY AS Avail_QTY,
T1.USER_NUM1,
CASE WHEN T2.HALT <> ' ' THEN 'Y' ELSE NULL END AS Halt,
T4.DESCRIPTION AS T4_Description,
det.OH_QTY AS Det_OH_QTY,
det.COM_QTY AS Det_COM_QTY,
DECODE (det.INSP_STAT, '3', 'Passed Inpection', DECODE det.INSP_STAT,'1','Waiting Inspection' ,' ')) as Inspect_Descr
, T3.RESV_QTY
from ITEM T1
LEFT OUTER JOIN ITEM_CCN T2
ON T1.ITEM=T2.ITEM
and T1.REVISION=T2.REVISION
LEFT OUTER JOIN ITEM_LOC T3
on T2.CCN=T3.CCN
and T2.ITEM=T3.ITEM
and T2.REVISION=T3.REVISION
LEFT OUTER JOIN HALT T4
on T2.HALT=T4.HALT
and T2.CCN=T4.CCN
LEFT OUTER JOIN ITEM_DET det
on T3.CCN=det.CCN
and T3.ITEM=det.ITEM
and T3.REVISION=det.REVISION
and T3.MAS_LOC=det.MAS_LOC
and T3.LOCATION=det.LOCATION
where T2.OBSOLETED is null and p_ViewAll = 'Y'
UNION ALL
SELECT T1.ITEM
, T1.REVISION
, T1.DESCRIPTION
, T2.CCN
, T2.DELETED
, T2.OBSOLETED
, T2.FINGOOD
, T2.ABC
, T3.MAS_LOC
, T3.LOCATION
, (T3.OH_QTY - T3.COM_QTY) - T3.RESV_QTY as Avail_QTY
, T1.USER_NUM1
, case when T2.HALT<>' ' then 'Y' else NULL end as Halt
, T4.DESCRIPTION as T4_Description
, det.OH_QTY as Det_OH_QTY
, det.COM_QTY as Det_COM_QTY
, DECODE(det.INSP_STAT,'3','Passed Inpection' ,DECODE det.INSP_STAT,'1','Waiting Inspection' ,' ')) as Inspect_Descr
, T3.RESV_QTY
from ITEM T1
LEFT OUTER JOIN ITEM_CCN T2
ON T1.ITEM=T2.ITEM
and T1.REVISION=T2.REVISION
LEFT OUTER JOIN ITEM_LOC T3
on T2.CCN=T3.CCN
and T2.ITEM=T3.ITEM
and T2.REVISION=T3.REVISION
LEFT OUTER JOIN HALT T4
on T2.HALT=T4.HALT
and T2.CCN=T4.CCN
LEFT OUTER JOIN ITEM_DET det
on T3.CCN=det.CCN
and T3.ITEM=det.ITEM
and T3.REVISION=det.REVISION
and T3.MAS_LOC=det.MAS_LOC
and T3.LOCATION=det.LOCATION
where T2.OBSOLETED is null and p_ViewAll = 'N'
and myfilterstuff = 'whatever'