Estrazione da tabella

USE tempdb;

CREATE TABLE dbo.foo(
id int NOT NULL,
[desc] varchar(3) NOT NULL,
period int NOT NULL
);

INSERT dbo.foo VALUES
      (1, 'ETA', 1)
    , (1, 'ETA', 2)
    , (1, 'ETA', 3)
    , (1, 'ETA', 4)
    , (1, 'ADA', 5)
    , (1, 'ADA', 6)
    , (1, 'ADA', 7)
    , (1, 'ADA', 8)
    , (2, 'ADA', 1)
    , (2, 'ADA', 2);

SELECT id, [desc], MAX(period) AS period
FROM dbo.foo
GROUP BY id, [desc];

/* Output:

id          desc period
----------- ---- -----------
1           ADA  8
2           ADA  2
1           ETA  4

(3 row(s) affected)

*/

DROP TABLE dbo.foo;