Question

Googling it a bit I found this to be an interesting question. Would like you guys shots.

Having my table

USER    |   MAP |   STARTDAY    |   ENDDAY
1       |   A   |   20110101    |   20110105
1       |   B   |   20110106    |   20110110
2       |   A   |   20110101    |   20110107
2       |   B   |   20110105    |   20110110

Whant I want is to fix user’s 2 case, where maps A and B overlaps by a couple days (from 20110105 until 20110107).
I wish I was able to query that table in a way that it never return overlapping ranges. My input data is falky already, so I don’t have to worry with the conflict treatment, I just want to be able to get a single value for any given BETWEEN these dates.

Possible outputs for the query I’m trying to build would be like

USER    |   MAP |   STARTDAY    |   ENDDAY
2       |   B   |   20110108    |   20110110 -- pushed overlapping days ahead..
2       |   A   |   20110101    |   20110104 -- shrunk overlapping range

It doesn’t even matter if the algorithm causes “invalid ranges”, e.g. Start = 20110105, End = 20110103, I’ll just put null when I get to these cases.

What would you guys say? Any straight forward way to get this done?

Thanks!

f.

Answer 1

Analytic functions could help:

select userid, map
, case when prevend >= startday then prevend+1 else startday end newstart
, endday
from
( select userid, map, startday, endday
  , lag(endday) over (partition by userid order by startday) prevend
  from mytable
)
order by userid, startday

Gives:

USERID  MAP     NEWSTART        ENDDAY
1       A       01/01/2011      01/05/2011
1       B       01/06/2011      01/10/2011
2       A       01/01/2011      01/07/2011
2       B       01/08/2011      01/10/2011