Convert fixed months, weeks or years to days in oracle

SELECT nvl(mfg_shelf_life, -1)
            ,nvl(mfg_shelf_life_timeframe,'x')
      FROM dss.part_specs pspec
      where mfg_shelf_life_timeframe in ('Y','W','M')

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shelf life
M - Months
Y   Years
W  Weeks.
 
Right now I do not have data with weeks.

I need to take that value and convert to days.  Can I get a query to get these values?
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anumosesAsked:
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PortletPaulfreelancerCommented:
This question differs slightly (I think) from the question made yesterday.

a. Yesterday the table involved building things
b. Here the table is manufacturer's specifications

for a. there has to be a date of receipt (or similar) otherwise you cannot build/repair
for b. the purpose may be comparisons and not involve any concrete date of receipt

Given that the topic under discussion is aircraft parts then (in my view) you need to be "conservative" (as lives are at risk) so I suggest:

a "year" is 365 days
a "month" is treated as 30 days (round down 365/12)
and a week obviously 7 days

Because the topic is aircraft parts there will probably be standards that apply but I am no longer part of the aerospace industry so I'm hopelessly out of date on those.

so, for approximations in the common unit of days:
SELECT
      part
    , mfg_shelf_life
    , mfg_shelf_life_timeframe
    , mfg_shelf_life 
      * ( case when mfg_shelf_life_timeframe = 'Y' then 365
               when mfg_shelf_life_timeframe = 'M' then 30
               when mfg_shelf_life_timeframe = 'W' then 7
          end ) 
                    AS mfg_shelf_life_in_days_approx
FROM dss.part_specs pspec
WHERE mfg_shelf_life_timeframe IN ('Y', 'W', 'M')

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sdstuberCommented:
The result is simple, it's just multiplication.

The tricky part is what to multiply by..

How long is a month?  28, 29, 30, 31 days? something else, if so what?
How long is a year?  365 or 366 days?  something else, if so what?
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awking00Commented:
Weeks are easy, they all have 7 days. But years and months are not fixed, you'll need to have dates in order to calculate days.
The days between 01-JAN-2016 and 01-JAN-2017 are 366 but the days between 01-JAN-2017 and 01-JAN-2018 are 365.
The days between 01-JAN-2016 and 01-MAR-2016 are 60 but the days between 01-JUL-2016 and 01-SEP-2016 are 62.
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sdstuberCommented:
Rather than multiplying, do you have a start date?  If so, we can use the actual calendar rather than make multiplicative approximations.
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johnsoneSenior Oracle DBACommented:
I posted those calculations in the question you asked yesterday.  You should be able to pull them out of the function, but if you can't, here they are:

weeks to days:

shelf_life_weeks * 7

months to days:

expire_date - Add_months(expire_date, shelf_life_months * -1)

years to days:

expire_date - Add_months(expire_date, shelf_life_years * -12)
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johnsoneSenior Oracle DBACommented:
Not sure why you need the calculations to convert to days, as the function that was posted yesterday took care of that calculation internally.  All you have to do is pass in the number of weeks/months/years and it figures it out.
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awking00Commented:
Okay. With expire_date and sysdate you have the dates you need to calculate days and johnsone gave you precisely what those calculations are.
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johnsoneSenior Oracle DBACommented:
Regardless of the field names, the math is the same.
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anumosesAuthor Commented:
Thanks.
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