SQL gaps in dates - sql

Question

I am trying to find gaps in the a table based on a state code the tables look like this.
StateTable:
StateID (PK) | Code
--------------------
1 | AK
2 | AL
3 | AR
StateModel Table:
StateModelID | StateID | EfftiveDate | ExpirationDate
-------------------------------------------------------------------------
1 | 1 | 2012-06-28 00:00:00.000| 2012-08-02 23:59:59.000
2 | 1 | 2012-08-03 00:00:00.000| 2050-12-31 23:59:59.000
3 | 1 | 2055-01-01 00:00:00.000| 2075-12-31 23:59:59.000
The query I am using is the following:
Declare #gapMessage varchar(250)
SET #gapMessage = ''
select
#gapMessage = #gapMessage +
(Select StateTable.Code FROM StateTable where t1.StateID = StateTable.StateID)
+ ' Row ' +CAST(t1.StateModelID as varchar(6))+' has a gap with '+
CAST(t2.StateModelID as varchar(6))+ CHAR(10)
from StateModel t1
inner join StateModel t2
on
t1.StateID = t2.StateID
and DATEADD(ss, 1,t1.ExpirationDate) < t2.EffectiveDate
and t1.EffectiveDate < t2.EffectiveDate
if(#gapMessage != '')
begin
Print 'States with a gap problem'
PRINT #gapMessage
end
else
begin
PRINT 'No States with a gap problem'
end
But with the above table example I get the following output:
States with a gap problem
AK Row 1 has a gap with 3
AK Row 2 has a gap with 3
Is there anyway to restructure my query so that the gap between 1 and 3 does not display because there is not a gap between 1 and 2?
I am using MS sql server 2008
Thanks

Answer 1

WITH
sequenced AS
(
SELECT
ROW_NUMBER() OVER (PARTITION BY StateID ORDER BY EfftiveDate) AS SequenceID,
*
FROM
StateModel
)
SELECT
*
FROM
sequenced AS a
INNER JOIN
sequenced AS b
ON a.StateID = b.StateID
AND a.SequenceID = b.SequenceID - 1
WHERE
a.ExpirationDate < DATEADD(second, -1, b.EfftiveDate)
To make this as effective as possible, also add an index on (StateID, EfftiveDate)

Answer 2

I wanted to just give credit to MatBailie, but don't have the points to do it yet, so I thought I would help out anyone else looking for a similar solution that may want to take it a step further like I needed to. I have changed my application of his code (which involves member enrollment) to the same language as the example here.
In my case, I needed these things:
I have two similar tables that I need to develop into one total table. In this example, let's make the tables like this: SomeStates + OtherStates = UpdatedTable. These are UNIONED in the AS clause.
I didn't want to remove any rows due to gaps, but I wanted to flag them on the StateID level. This is added as an additional column 'StateID_GapFlag'.
I also wanted to add a column to hold the oldest or MIN(EffectiveDate). This would be used in later calculations of SUM(period) to get a total duration, excluding gaps. This is the column 'MIN_EffectiveDate'.
;WITH sequenced
( SequenceID
,EffectiveDate
,ExpirationDate)
AS
(select
ROW_NUMBER() OVER (PARTITION BY StateID ORDER by EffectiveDate) as SequenceID,
* from (select EffectiveDate, ExpirationDate from SomeStates
UNION ALL
(select EffectiveDate, ExpirationDate from OtherStates)
) StateModel
where
EffectiveDate > 'filter'
)
Select DISTINCT
IJ1.[MIN_EffectiveDate]
,coalesce(IJ2.GapFlag,'') as [MemberEnrollmentGapFlag]
,EffectiveDate
,ExpirationDate
into UpdatedTable
from sequenced seq
inner join
(select StateID, min(EffectiveDate) as 'MIN_EffectiveDate'
from sequenced
group by StateID
) IJ1
on seq.member# = IJ1.member
left join
(select a.member#, 'GAP' as 'StateID_GapFlag'
from sequenced a
inner join
sequenced b
on a.StateID = b.StateID
and a.SequenceID = (b.sequenceID - 1)
where a.ExpirationDate < DATEADD(day, -1, b.EffectiveDate)
) LJ2
on seq.StateID = LJ2.StateID

Answer 3

You could use ROW_NUMBER to provide an ordering of stateModel's for each state, then check that the second difference for consecutive rows doesn't exceed 1. Something like:
;WITH Models (StateModelID, StateID, Effective, Expiration, RowOrder) AS (
SELECT StateModelID, StateID, EffectiveDate, ExpirationDate,
ROW_NUMBER() OVER (PARTITION BY StateID, ORDER BY EffectiveDate)
FROM StateModel
)
SELECT F.StateModelId, S.StateModelId
FROM Models F
CROSS APPLY (
SELECT M.StateModelId
FROM Models M
WHERE M.RowOrder = F.RowOrder + 1
AND M.StateId = F.StateId
AND DATEDIFF(SECOND, F.Expiration, M.Effective) > 1
) S
This will get you the state model IDs of the rows with gaps, which you can format how you wish.