Can a view include a variable

Question

So what I'm trying to do is create a modified version of a view that can accept a date range when run. I have come across references to "parameterized views" and views using "context variables". Can someone help me understand the difference between the two and which approach is better for my situation?
Here is a sample of one working view (there are dozens):
CREATE OR REPLACE FORCE VIEW  "VF_PAYLOAD_BYMONTH"
  ("FACTORY_ID", "MONTH", "LOADS",
      "TTL_BIDTONS", "AVGBIDPAYLOAD",
      "TTL_ACTTONS", "AVGACTPAYLOAD") AS
  (select FACTORY_ID, to_number(to_char(DT,'MMYYYY')), SUM(LDS),
      SUM(TTL_BID_TONS), AVG(AVG_BID_TONS), SUM(TTL_ACT_TONS), AVG(AVG_ACT_TONS) from
  (select j.FACTORY_ID, c.DATE_INDEX as DT, COUNT(j.LOAD_JOB_ID) as LDS,
        SUM(DECODE(r.BID_TONS,0,NULL,r.BID_TONS)) as TTL_BID_TONS,
        AVG(DECODE(r.BID_TONS,0,NULL,r.BID_TONS)) as AVG_BID_TONS,
        SUM(DECODE(w.SPOT_WEIGHT,0,j.MAN_SPOT_WT,w.SPOT_WEIGHT)) as TTL_ACT_TONS,
        AVG(DECODE(w.SPOT_WEIGHT,0,j.MAN_SPOT_WT,w.SPOT_WEIGHT)) as AVG_ACT_TONS
     from TC c, TC_LOAD_JOBS j, LOAD_RATES r, SPOT_WEIGHTS w
    where c.TC_ID = j.TC_ID and j.LOAD_RATE_ID = r.LOAD_RATE_ID and r.YARD = 0
      and c.DATE_INDEX = w.DATE_INDEX and j.LOAD_RATE_ID = w.LOAD_RATE_ID
    group by j.FACTORY_ID, c.DATE_INDEX)
  group by FACTORY_ID, to_number(to_char(DT,'MMYYYY')))
/This is what I am after:
CREATE OR REPLACE FORCE VIEW  "VF_PAYLOAD_BYMONTH"
  ("FACTORY_ID", "MONTH", "LOADS",
      "TTL_BIDTONS", "AVGBIDPAYLOAD",
      "TTL_ACTTONS", "AVGACTPAYLOAD") AS
  (select FACTORY_ID, to_number(to_char(DT,'MMYYYY')), SUM(LDS),
      SUM(TTL_BID_TONS), AVG(AVG_BID_TONS), SUM(TTL_ACT_TONS), AVG(AVG_ACT_TONS) from
  (select j.FACTORY_ID, c.DATE_INDEX as DT, COUNT(j.LOAD_JOB_ID) as LDS,
        SUM(DECODE(r.BID_TONS,0,NULL,r.BID_TONS)) as TTL_BID_TONS,
        AVG(DECODE(r.BID_TONS,0,NULL,r.BID_TONS)) as AVG_BID_TONS,
        SUM(DECODE(w.SPOT_WEIGHT,0,j.MAN_SPOT_WT,w.SPOT_WEIGHT)) as TTL_ACT_TONS,
        AVG(DECODE(w.SPOT_WEIGHT,0,j.MAN_SPOT_WT,w.SPOT_WEIGHT)) as AVG_ACT_TONS
     from TC c, TC_LOAD_JOBS j, LOAD_RATES r, SPOT_WEIGHTS w
    where c.TC_ID = j.TC_ID and j.LOAD_RATE_ID = r.LOAD_RATE_ID and r.YARD = 0
      and c.DATE_INDEX = w.DATE_INDEX and j.LOAD_RATE_ID = w.LOAD_RATE_ID
      and c.DATE_INDEX between :X and :Y   <-----  ADDED THIS
    group by j.FACTORY_ID, c.DATE_INDEX)
  group by FACTORY_ID, to_number(to_char(DT,'MMYYYY')))
/What I'd like to do is place a date range on the underlying query. The user wants two versions of the report: one that grabs everything by month and one that grabs everything by month but only within a certain date range.
PS. If this is possible, how do I "call" the view?

Answer 1

re Centinul : This is actually getting called using a procedure in APEX to generate a report. The entire report consists of one or more of these procedures: each one calculates a year's worth of metrics related to a given category and the data comes from a variety of source tables. I used views to ease the creation of the procedures, but maybe that's the wrong way to go. The thing is that the data has to be condensed (the view) then translated from rows into columns (handled in SQL in procedure) because I am on 10g (I don't have the PIVOT capability in 11g which would REALLY help simplify these reports a LOT). Putting it into views makes it easier to keep track of what is going on.
re Ajay Sharma, bluefrog, and AP: Yes, I saw those. Spent half an hour on AskTom, but the thing I didn't see was just a basic explanation of purpose and how to use it. The articles I saw kind of skipped that part, which was why I was asking here for an explanation.
re Frank Kulash: Thanks for the detailed explanation. As the view is going to be referenced from APEX, which shares a common execution user, I am questioning whether the parameterized approach would work at all, but I would appreciate input. It is looking more and more like I am going to have to incorporate the view directly into the procedure, as I will likely have more than one user attempting to access this report at the same time.
Any other suggestions would be appreciated. Here is the query being used in the procedure. Please understand that this is one of the simple ones: several of the other views are composites formed from two, three, or even four base views. Manageability quickly becomes a major concern here.
cursor c_PYLD_TARGET is SELECT NVL(SUM(CASE WHEN MONTH = to_number('08'||(v_dt-1))
          THEN AVGBIDPAYLOAD END),0) as "AUG",
        NVL(SUM(CASE WHEN MONTH = to_number('09'||(v_dt-1))
          THEN AVGBIDPAYLOAD END),0) as "SEP",
        NVL(SUM(CASE WHEN MONTH = to_number('10'||(v_dt-1))
          THEN AVGBIDPAYLOAD END),0) as "OCT",
        NVL(SUM(CASE WHEN MONTH = to_number('11'||(v_dt-1))
          THEN AVGBIDPAYLOAD END),0) as "NOV",
        NVL(SUM(CASE WHEN MONTH = to_number('12'||(v_dt-1))
          THEN AVGBIDPAYLOAD END),0) as "DEC",
        NVL(SUM(CASE WHEN MONTH = to_number('01'||v_dt)
          THEN AVGBIDPAYLOAD END),0) as "JAN",
        NVL(SUM(CASE WHEN MONTH = to_number('02'||v_dt)
          THEN AVGBIDPAYLOAD END),0) as "FEB",
        NVL(SUM(CASE WHEN MONTH = to_number('03'||v_dt)
          THEN AVGBIDPAYLOAD END),0) as "MAR",
        NVL(SUM(CASE WHEN MONTH = to_number('04'||v_dt)
          THEN AVGBIDPAYLOAD END),0) as "APR",
        NVL(SUM(CASE WHEN MONTH = to_number('05'||v_dt)
          THEN AVGBIDPAYLOAD END),0) as "MAY",
        NVL(SUM(CASE WHEN MONTH = to_number('06'||v_dt)
          THEN AVGBIDPAYLOAD END),0) as "JUN",
        NVL(SUM(CASE WHEN MONTH = to_number('07'||v_dt)
          THEN AVGBIDPAYLOAD END),0) as "JUL"
     from VF_PAYLOAD_BYMONTH
    where FACTORY_ID = v_proj;
...(might help to get the right one)
Edited by: blarman74 on Aug 24, 2010 11:10 AM