问题
Hi I am using DB2 sql to fill in some missing data in the following table:
Person House From To
------ ----- ---- --
1 586 2000-04-16 2010-12-03
2 123 2001-01-01 2012-09-27
2 NULL NULL NULL
2 104 2004-01-01 2012-11-24
3 987 1999-12-31 2009-08-01
3 NULL NULL NULL
Where person 2 has lived in 3 houses, but the middle address it is not known where, and when. I can't do anything about what house they were in, but I would like to take the previous house they lived at, and use the previous To date to replace the NULL From date, and use the next address info and use the From date to replace the null To date ie.
Person House From To
------ ----- ---- --
1 586 2000-04-16 2010-12-03
2 123 2001-01-01 2012-09-27
2 NULL 2012-09-27 2004-01-01
2 104 2004-01-01 2012-11-24
3 987 1999-12-31 2009-08-01
3 NULL 2009-08-01 9999-01-01
I understand that if there is no previous address before a null address, that will have to stay null, but if a null address is the last know address I would like to change the To date to 9999-01-01 as in person 3.
This type of problem seems to me where set theory no longer becomes a good solution, however I am required to find a DB2 solution because that's what my boss uses!
any pointers/suggestions welcome.
Thanks.
回答1:
It might look something like this:
select
person,
house,
coalesce(from_date, prev_to_date) from_date,
case when rn = 1 then coalesce (to_date, '9999-01-01')
else coalesce(to_date, next_from_date) end to_date
from
(select person, house, from_date, to_date,
lag(to_date) over (partition by person order by from_date nulls last) prev_to_date,
lead(from_date) over (partition by person order by from_date nulls last) next_from_date,
row_number() over (partition by person order by from_date desc nulls last) rn
from temp
) t
The above is not tested but it might give you an idea.
I hope in your actual table you have a column other than to_date and from_date that allows you to order rows for each person, otherwise you'll have trouble sorting NULL dates, as you have no way of knowing the actual sequence.
回答2:
create table Temp
(
person varchar(2),
house int,
from_date date,
to_date date
)
insert into temp values
(1,586,'2000-04-16','2010-12-03 '),
(2,123,'2001-01-01','2012-09-27'),
(2,NULL,NULL,NULL),
(2,104,'2004-01-01','2012-11-24'),
(3,987,'1999-12-31','2009-08-01'),
(3,NULL,NULL,NULL)
select A.person,
A.house,
isnull(A.from_date,BF.to_date) From_date,
isnull(A.to_date,isnull(CT.From_date,'9999-01-01')) To_date
from
((select *,ROW_NUMBER() over (order by (select 0)) rownum from Temp) A left join
(select *,ROW_NUMBER() over (order by (select 0)) rownum from Temp) BF
on A.person = BF.person and
A.rownum = BF.rownum + 1)left join
(select *,ROW_NUMBER() over (order by (select 0)) rownum from Temp) CT
on A.person = CT.person and
A.rownum = CT.rownum - 1
来源：https://stackoverflow.com/questions/17293073/fill-in-a-null-cell-with-cell-from-previous-record