Thank you Oleg, I am curious about uniquely identifying rows in tables w/o PKs (sorry about the off topic).

I mean, as I understand from your explanation there is some "row id" that we have no access to, and it´s managed by the dbms.

If that is the case, let's assume a table with 2 int cols, with no primary key, and then you store 5 times the same values, ie:

create table t2 (a int, b int)

insert into t2 values (1,1)

insert into t2 values (1,1)

insert into t2 values (1,1)

insert into t2 values (1,1)

How can you actually uniquely identify one of those rows let's say if i want to delete only one of those?

I've tryed doing it with enterprise manager, but got an error such as "wrong primary key or insufficcient column information".

Sorry about the weird case, i'm a student just taking DB course :p