SQL Server 2012 Retrieving Attributes for 2 Columns of a Table

Question

I have the following tables.

Highschooler

Friends

And ID1 and ID2 are IDs (they are not the same) in the ID column of Highschooler. How can I select grades for both of these columns so I have something like:

ID1   Grade    ID2   Grade

Answer 1

You should join Friends with Highschooler two times (for each ID column)

select t1.ID1
     , t2.grade
     , t1.ID2
     , t3.grade
from Friends t1 
join Highschooler t2 on t1.ID1 = t2.ID 
join Highschooler t3 on t1.ID2 = t3.ID