Hello,
I know relational algebra uses sets which eliminates duplicates values but I'm not sure about one thing.
Duplicate values are impossible to exist in a relation ever?
For example I can never have a relation R(A,B) with values (1,2),(1,2) ?
Or they get eliminated <b>after</b> a projection or selection, so when I do for example projA(R) <b>then</b> they get eliminated?
Thank you.