troubles with next and previous query - sql

Question

I have a list and the returned table looks like this. I took the preview of only one car but there are many more.
What I need to do now is check that the current KM value is larger then the previous and smaller then the next. If this is not the case I need to make a field called Trustworthy and should fill it with either 1 or 0 (true/ false).
The result that I have so far is this:
validKMstand and validkmstand2 are how I calculate it. It did not work in one list so that is why I separated it.
In both of my tries my code does not work.
Here is the code that I have so far.
FullList as (
SELECT
*
FROM
eMK_Mileage as Mileage
)
, ValidChecked1 as (
SELECT
UL1.*,
CASE WHEN EXISTS(
SELECT TOP(1)UL2.*
FROM FullList AS UL2
WHERE
UL2.FK_CarID = UL1.FK_CarID AND
UL1.KM_Date > UL2.KM_Date AND
UL1.KM > UL2.KM
ORDER BY UL2.KM_Date DESC
)
THEN 1
ELSE 0
END AS validkmstand
FROM FullList as UL1
)
, ValidChecked2 as (
SELECT
List1.*,
(CASE WHEN List1.KM > ulprev.KM
THEN 1
ELSE 0
END
) AS validkmstand2
FROM ValidChecked1 as List1 outer apply
(SELECT TOP(1)UL3.*
FROM ValidChecked1 AS UL3
WHERE
UL3.FK_CarID = List1.FK_CarID AND
UL3.KM_Date <= List1.KM_Date AND
List1.KM > UL3.KM
ORDER BY UL3.KM_Date DESC) ulprev
)
SELECT * FROM ValidChecked2 order by FK_CarID, KM_Date

Answer 1

Maybe something like this is what you are looking for?
;with data as
(
select *, rn = row_number() over (partition by fk_carid order by km_date)
from eMK_Mileage
)
select
d.FK_CarID, d.KM, d.KM_Date,
valid =
case
when (d.KM > d_prev.KM /* or d_prev.KM is null */)
and (d.KM < d_next.KM /* or d_next.KM is null */)
then 1 else 0
end
from data d
left join data d_prev on d.FK_CarID = d_prev.FK_CarID and d_prev.rn = d.rn - 1
left join data d_next on d.FK_CarID = d_next.FK_CarID and d_next.rn = d.rn + 1
order by d.FK_CarID, d.KM_Date
With SQL Server versions 2012+ you could have used the lag() and lead() analytical functions to access the previous/next rows, but in versions before you can accomplish the same thing by numbering rows within partitions of the set. There are other ways too, like using correlated subqueries.
I left a couple of conditions commented out that deal with the first and last rows for every car - maybe those should be considered valid is they fulfill only one part of the comparison (since the previous/next rows are null)?