So i have a table of readings (heavily simplified version below) - sometimes there is a break in the reading history (see the record i have flagged as N) - The 'From Read' should always match a previous 'To Read' or the 'To Read' should always match a later 'From Read' BUT I want to only select records as far back as the first 'break' in the reads.
How would i write a query in DB2 SQL to only return the rows flagged with a 'Y'?
EDIT: The contiguous flag is something i have added manually to represent the records i would like to select, it does not exist on the table.
ID From To Contiguous
ABC 01/01/2014 30/06/2014 Y
ABC 01/06/2013 01/01/2014 Y
ABC 01/05/2013 01/06/2013 Y
ABC 01/01/2013 01/02/2013 N
ABC 01/10/2012 01/01/2013 N
Thanks in advance! J
you will need a recursive select something like that:
WITH RECURSIVE
contiguous_intervals(start, end) AS (
select start, end
from intervals
where end = (select max(end) from intervals)
UNION ALL
select i.start, i.end
from contiguous_intervals m, intervals i
where i.end = m.start
)
select * from contiguous_intervals;
You can do this with lead()
, lag()
. I'm not sure what the exact logic is for your case, but I think it is something like:
select r.*,
(case when (prev_to = from or prev_to is null) and
(next_from = to or next_from is null)
then 'Y'
else 'N'
end) as Contiguous
from (select r.*, lead(from) over (partition by id order by from) as next_from,
lag(to) over (partition by id order by to) as prev_to
from readings r
) r;
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