Finding point of interest on a square wave using sql - sql-server

Question

Good day,
I have a sql table with the following setup:
DataPoints{ DateTime timeStampUtc , bit value}
The points are on a minute interval, and store either a 1(on) or a 0(off).
I need to write a stored procedure to find the points of interest from all the data points.
I have a simplified drawing below:
I need to find the corner points only. Please note that there may be many data points between a value change. For example:
{0,0,0,0,0,0,0,1,1,1,1,0,0,0}
This is my thinking atm (high level)
Select timeStampUtc, Value
From Data Points
Where Value before or value after differs by 1 or -1
I am struggling to convert this concept to sql, and I also have a feeling there is an more elegant mathematical solution that I am not aware off. This must be a common problem in electronics?

Answer 1

I have wrapped the table into a CTE. Then, I am joining every row in the CTE to the next row of itself. Also, I've added a condition that the consequent rows should differ in the value.
This would return you all rows where the value changes.
;WITH CTE AS(
SELECT ROW_NUMBER() OVER(ORDER BY TimeStampUTC) AS id, VALUE, TIMESTAMPUTC
FROM DataPoints
)
SELECT CTE.TimeStampUTC as "Time when the value changes", CTE.id, *
FROM CTE
INNER JOIN CTE as CTE2
ON CTE.id = CTE2.id + 1
AND CTE.Value != CTE2.Value
Here's a working fiddle: http://sqlfiddle.com/#!6/a0ddc/3

Answer 2

If I got it correct, you are looking for something like this:
with cte as (
select * from (values (1,0),(2,0),(3,1),(4,1),(5,0),(6,1),(7,0),(8,0),(9,1)) t(a,b)
)
select
min(a), b
from (
select
a, b, sum(c) over (order by a rows unbounded preceding) grp
from (
select
*, iif(b = lag(b) over (order by a), 0, 1) c
from
cte
) t
) t
group by b, grp