On 28-Jun-2016 15:50 -0500, Bill Howie wrote:
[…] I have a field in a file that is a date (field is in packed
format). The date in the field looks like this: 1160628.
Assumed: DEC(7) representing a /date/ value in form CYYMMDD.
The need is to only grab records from this file that go back 3 months
from the first day of the current month, so in this case I'd only
want records with a date greater than 1160301. This also needs to
work if when subtracting the 3 months I had to go across multiple
years. I know I can do a formula something like this:
(CURRENT_DATE - (DAY(CURRENT_DATE)-1) DAYS - 3 MONTH)
But I'm not sure how to use the packed numeric date field I have to
get there. Any thoughts would be greatly appreciated. Thanks!
Consider the following scripted actions as means to address the issue
as presented, and learn by tests performed, what was created:
Create some effective casting functions, between DATE data type and
the DEC(7) as CYYMMDD:
create function D7cymdToDate
( d7cymd dec(7)
) returns date
language sql
return
date( digits(dec((19000000 + d7cymd), 8)) concat '000000' )
;
create function DateToD7cymd
( inpDate date
) returns dec(7)
language sql
return
replace(char(inpDate, ISO), '-', '') - 19000000
;
Create a function to determine the starting date from the past N
months, according to the expression given:
create function months_past
( inpDate date
, nbrMonths int
) returns date
language sql
return
(inpDate - (DAY(inpDate)-1) DAYS - nbrMonths MONTH)
;
Note: the above UDFs were created with no exception handling nor any
thought as to the default settings [e.g. deterministic]; having only a
RETURN statement, they should be capable of being /inlined/
Create a table with some data for testing; include some data for
selecting into prior year and into prior century, and have a true DATE
type value alongside each CYYMMDD DEC(7) value:
create table d7test
( d7cymd dec(7)
, d7date date
)
;
insert into d7test (d7cymd) values
( 0990930 ), ( 0991001 ), ( 0991031 ), ( 0991101 ), ( 0991130 )
, ( 1150930 ), ( 1151001 ), ( 1151031 ), ( 1151101 ), ( 1151130 )
, ( 1160630 ), ( 1160701 ), ( 1160731 ), ( 1160801 ), ( 1160831 )
;
insert into d7test (d7date) values
( '1999-09-15' ), ( '1999-10-15' ), ( '1999-11-15' )
, ( '2015-09-15' ), ( '2015-10-15' ), ( '2015-11-15' )
, ( '2016-01-15' ), ( '2016-02-15' ), ( '2016-03-15' )
, ( '2016-04-15' ), ( '2016-05-15' ), ( '2016-06-15' )
, ( '2016-07-15' ), ( '2016-08-15' ), ( '2016-09-15' )
, ( '2016-10-15' ), ( '2016-11-15' ), ( '2016-12-15' )
; -- a mid-month date value for all of 2016; test into 2017
update d7test set d7date = D7cymdToDate(d7cymd)
where d7date is null
;
update d7test set d7cymd = DateToD7cymd(d7date)
where d7cymd is null
;
Now perform some tests; to limit the results, each where-clause adds
an extra predicate for d7date being less than the date that is supplied
as input to the months_past UDF on the pertinent predicate:
• verify selection on prior-year; use a date constant vs special
register:
select d7cymd , d7date
from d7test
where d7cymd > DateToD7cymd( months_past( date'2016-01-28', 3 ) )
and d7date<date'2016-01-28'
order by d7date
; -- result: six rows, since 2015-10-15
• verify selection on prior-century year; use a date constant vs the
special register:
select d7cymd , d7date
from d7test
where d7cymd > DateToD7cymd( months_past( date'2000-01-28', 3 ) )
and d7date<date'2000-01-28'
order by d7date
; -- result: five rows, since 1999-10-15
• a less desirable selection prohibits key selection:
select d7cymd , d7date
from d7test
where D7cymdToDate(d7cymd) > months_past( current_date, 3 )
and d7date<current_date
order by d7date
; -- if run in jun-2016, result: four rows, since 2016-03-15
• a more desirable selection to allow keyed selection:
select d7cymd , d7date
from d7test
where d7cymd > DateToD7cymd( months_past( current_date, 3 ) )
and d7date<current_date
order by d7date
; -- if run in jun-2016, result: four rows, since 2016-03-15
midrange.com
