There is a table:

CREATE TABLE temp
(
   IDR decimal(9) NOT NULL,
   IDS decimal(9) NOT NULL,
   DT date NOT NULL,
   VAL decimal(10) NOT NULL,
   AFFID decimal(9),
   CONSTRAINT PKtemp PRIMARY KEY (IDR,IDS,DT)
)
;     
SQL>explain plan for select * from temp;

Explained.

SQL> select plan_table_output from table(dbms_xplan.display('plan_table',null,'serial'));

PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------

---------------------------------------------------------------
| Id  | Operation     | Name | Rows  | Bytes | Cost (%CPU)|
---------------------------------------------------------------
|   0 | SELECT STATEMENT  |   |     1 |    61 |     2   (0)|
|   1 |  TABLE ACCESS FULL| TEMP |     1 |    61 |     2   (0)|
---------------------------------------------------------------

Note
-----
   - 'PLAN_TABLE' is old version

11 rows selected.

SQL server 2008 shows in the same situation Clustered index scan. What is the reason?