USE tempdb;

CREATE TABLE dbo.Studenti(
CodiceFiscale char(16) NOT NULL,
Nome varchar(10) NOT NULL,
Cognome varchar(10) NOT NULL,
CONSTRAINT PK_Studenti PRIMARY KEY (CodiceFiscale)
);

INSERT dbo.Studenti VALUES('BNGLNZ71H12M052S', 'Lorenzo', 'Benaglia');

/* Output:

(1 row(s) affected)

*/

INSERT dbo.Studenti VALUES('BNGLNZ71H12M052S', 'Lorenzo', 'Benaglia');

/* Output:

Msg 2627, Level 14, State 1, Line 1
Violation of PRIMARY KEY constraint 'PK_Studenti'. Cannot insert duplicate key in object 'dbo.Studenti'.
The statement has been terminated.

*/

SELECT *
FROM dbo.Studenti;

/* Output:

CodiceFiscale    Nome       Cognome
---------------- ---------- ----------
BNGLNZ71H12M052S Lorenzo    Benaglia

(1 row(s) affected)

*/

DROP TABLE dbo.Studenti;