Need to get common users to multiple users mapped to it - forum topic by Ram912

Hi,
I have a table which has one user ID mapped to multiple user IDs. I want to get the common user IDs mapped to each of the two user IDs
My Data looks in the following way

User ID	User ID 1
1	2
1	3
1	4
1	5
1	6
1	7
1	8
1	9
2	1
2	3
2	5
2	7
2	9
2	11
2	13
2	15
2	17
.	.
.	.
.	.
.	.
.	.
.	.
2000	
2001

I need to get for every User ID combination starting from (1,2) till (1999,2000) how many common User ID1's are there
Thanks in advance for any solution