Regroup data before sum

I'm a beginner with SQL Queries but I made this simple query which output the following data:

select ID, Length, Weight
from MyTable
where Group in('A1', 'A2')

What I would like to do is to group the lines by ID and Length and then only sum of all the data in the Weight column.

So basically I would get :

and then return the sum of the weight column.

This sounds simple but I can't manage to make it work...

Any Idea ?
Thank you in advance

Assume lenght 0,604 mean 0.604 in your problem description, a group by operator and sum() function should be able to get what your want, and then use SQL window function to all weight sum added to each line.

See the following code as an example:

select ID, Lenght, 
sum(Weight) as toal_weight_per_line,
SUM(SUM(weight)) OVER() as all_weight
from record
GROUP BY ID, Lenght
ORDER BY ID, Lenght

VERIFIED RUNNING EXAMPLE SQLFIDDLE LINK

Another method is to use CROSS JOIN operator

See the following code as example:

SELECT
    per_line.ID,
    per_line.Lenght,
    per_line.toal_weight_per_line,
    total.all_weight
FROM
(
    select ID, Lenght, 
    sum(Weight) as toal_weight_per_line
    from record
    GROUP BY ID, Lenght
) per_line
cross join
(
    select sum(weight) as all_weight
    FROM
    record
) total
ORDER BY ID, Lenght

VERIFIED RUNNING EXAMPLE SQLFIDDLE LINK

Does this answer your problem?

SELECT ID, Length, SUM(Weight) AS TotalWeight
FROM MyTable
WHERE Group IN ('A1', 'A2')
GROUP BY ID, Length