I have a table, that contains employees. Since the company I\'m working for is quite big (>3k employees) It is only natural, that some of them have the same names. Now they
Adding the flag to Daniel's answer...
SELECT NAME, SURNAME, USERNAME, DECODE(COUNT(*) OVER (PARTITION BY NAME, SURNAME), 1, 'N', 'Y') FROM YOUR_TABLE;
Please note that Oracle SQL has no support for booleans (sigh...)