How do I sum rows of a column based on 2 other column values?

[SAS49]

ID1	ID2	Length
A_001	A_005	450
A_001	A_005	600
A_001	A_005	700
A_001	A_006	350
A_001	A_006	800
A_005	A_006	900
A_005	A_006	750

Hi all, I am very new to SAS.  I have a data table of comparisons between 2 different IDs (found in columns 1 and 2), and the lengths shared between them.   There are multiple lengths listed for these different pairs.  I want the sum of lengths for each of the matching pairs and to output that as a separate data table.  See the example below: 

ID1	ID2	Length
A_001	A_005	1750
A_001	A_006	1150
A_005	A_006	1650

How would I accomplish this in SAS?  I honestly have no idea where even to start.  I appreciate any advice!  I am working in SAS 9.4. 

[PaigeMiller · Accepted solution]

I would let PROC SUMMARY have all the fun.

proc summary data=have nway;
    class id1 id2;
    var length;
    output out=want sum=;
run;

[tarheel13]

proc sql;
create table want as
select id1, id2, sum(length) as length
from have 
group by id1, id2;
quit;