How to Compare one row with other rows in SQL - sql

Question

I have a data set that consist of team members.
I want to calculate the Average of only member 2.
However, there are conditions for the calculation to meet like,
for example, id 1 have Anna and Sam working together, I want to calculate only for member2 which is Sam
For that, I want to sum the score of the ID's that have
Sam working with him self like id:2 member1:Sam member2:Sam
Sam working with other member but not Anna(member1) like id:3 member1:Sam member2:Nihal OR id:4 member1:Nihal member2:Sam
Then divide by distinct #ID
Input
+----+---------+---------+-------+
| ID | member1 | member2 | score |
+----+---------+---------+-------+
| 1 | Anna | Sam | 10 |
| 2 | Sam | Sam | 30 |
| 3 | Sam | Nihal | 40 |
| 4 | Nihal | Sam | 50 |
| 5 | Sam | Anna | 20 |
| 6 | Anna | Anna | 60 |
| 7 | Nihal | May | 70 |
| 8 | May | May | 80 |
+----+---------+---------+-------+
Output
+----+---------+---------+-------+-----+
| ID | member1 | member2 | score | AVG |
+----+---------+---------+-------+-----+
| 1 | Anna | Sam | 10 | 40 |-->AVG= 30+40+50/3
| 2 | Sam | Sam | 30 | 30 |-->AVG= score
| 3 | Sam | Nihal | 40 | 70 |-->AVG= 70/1
| 4 | Nihal | Sam | 50 | 20 |-->AVG= 30+10+20/3
| 5 | Sam | Anna | 20 | 60 |-->AVG= 60/1
| 6 | Anna | Anna | 60 | 60 |-->AVG= score
| 7 | Nihal | May | 70 | 80 |-->AVG= 80/1
| 8 | May | May | 80 | 80 |-->AVG= score
+----+---------+---------+-------+-----+

Answer 1

Try the following:
select t1.*,q.avg_score
from yourtable t1
cross apply
(
select avg(score) as avg_score
from yourtable t2
where
t1.member2 in (t2.member1,t2.member2)
and t1.member1 not in (t2.member1,t2.member2)
)q