Say, I have this simple table:

declare @t table ([period] date, [contract] int, price int);
insert into @t values
('2022-11-01', 1, 234),
('2022-12-01', 1, 277),
('2023-01-01', 1, 489),
('2022-11-01', 2, 187),
('2022-12-01', 2, 598),
('2022-03-01', 2, 478);

When using it as window function with and without ORDER BY , I get different results. When I used ORDER BY , I was surprised with the results since I expected all values in count column to be 3 .

select     *,
       count = count(*) over (partition by [contract] order by [period])
from @t;

I couldn't understand, why this was happening. Then I decided to remove order by [period] clause. And then all worked like a charm!

select     *,
       count = count(*) over (partition by [contract])
from @t;

After that I decided to take a look at the documentation, and it says:
The order_by_clause determines the logical order of the operation. See OVER clause (Transact-SQL) for more information.

And thatOVER link says:

ROWS/RANGE that limits the rows within the partition by specifying start and end points within the partition. It requires ORDER BY argument and the default value is from the start of partition to the current element if the ORDER BY argument is specified.

Do I correctly understand that as soon as I specify ORDER BY , it acts like BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW ? Then when I omit it, why it acts as BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING ?