Question

Ive got table:
UserA,
UserB,
numberOfConnections

I would like to write query which returns me only rows that has no reverse I mean or example :
for data :

1 2 10
1 3 10
1 5 10
1 6 10
2 6 10
2 5 10
5 1 10
5 2 10
3 1 10

it should return

1 2 10
1 3 10
1 5 10
1 6 10
2 6 10
2 5 10

rows:

5 1 10
5 2 10
3 1 10

arent valid because there are already corresponding

1 5 10
2 5 10
3 1 10

thanks for help
bye

Answer 1

This will do what you want

SELECT mt1.UserA, mt1.UserB, mt1.numberOfConnections
FROM MyTable mt1
LEFT OUTER JOIN MyTable mt2 ON mt1.UserA = mt2.UserB
        AND mt1.UserB = mt2.UserA
WHERE mt2.UserA IS NULL
    OR mt1.UserA < mt2.UserA