Rolling Average in sqlite - sql

Question

I want to calculate a rolling average in a table and keep track of the starting time of each calculated window frame.
My problem is, that I expect result count reduced compared of the rows in the table. But my query retuns the exact same row number. I think I understand why it does not work, but I don't know the remedy.
Let's say I have a table with example data that looks like this:
+------+-------+
| Tick | Value |
+------+-------+
| 1 | 1 |
| 2 | 3 |_
| 3 | 5 |
| 4 | 7 |_
| 5 | 9 |
| 6 | 11 |_
| 7 | 13 |
| 8 | 15 |_
| 9 | 17 |
| 10 | 19 |_
+------+-------+
I want to calculate the average of every nth item, for example of two rows (see marks above) so that I get an result of:
+--------------+--------------+
| OccurredTick | ValueAverage |
+--------------+--------------+
| 1 | 2 |
| 3 | 6 |
| 5 | 10 |
| 7 | 14 |
| 9 | 18 |
+--------------+--------------+
I tried that with
SELECT
FIRST_VALUE(Tick) OVER (
ROWS BETWEEN CURRENT ROW AND 2 FOLLOWING
) OccurredTick,
AVG(Value) OVER (
ROWS BETWEEN CURRENT ROW AND 2 FOLLOWING
) ValueAverage
FROM TableName;
What I get in return is:
+--------------+--------------+
| OccurredTick | ValueAverage |
+--------------+--------------+
| 1 | 2 |
| 2 | 4 |
| 3 | 6 |
| 4 | 8 |
| 5 | 10 |
| 6 | 12 |
| 7 | 14 |
| 8 | 16 |
| 9 | 18 |
| 10 | 19 |
+--------------+--------------+

Answer 1

You could use aggregation. If tick is always increasing with no gaps:
select min(tick), avg(value) avg_value
from mytable
group by cast((tick - 1) / 2 as integer)
You can change 2 to whatever group size suits to best.
If tick are not sequentially increasing, we can generate a sequence with row_number()
select min(tick), avg(value) avg_value
from (
select t.*, row_number() over(order by tick) rn
from mytable t
) t
group by cast((rn - 1) / 2 as integer)