----------------------------------------------------------

　　0 SELECT STATEMENT Optimizer=HINT: FIRST_ROWS (Cost=826 Card=20 Bytes=1840)

　　1 0 VIEW (Cost=826 Card=20 Bytes=1840)

　　2 1 COUNT (STOPKEY)

　　3 2 VIEW (Cost=826 Card=6361 Bytes=502519)

　　4 3 TABLE ACCESS (BY INDEX ROWID) OF 'T' (Cost=826 Card=6361 Bytes=133581)

　　5 4 INDEX (FULL SCAN) OF 'IND_T_OBJECT_NAME' (NON-UNIQUE) (Cost=26 Card=6361)

　　Statistics

　　----------------------------------------------------------

　　0 recursive calls

　　0 db block gets

　　22 consistent gets

　　0 physical reads

　　0 redo size

　　673 bytes sent via SQL*Net to client

　　503 bytes received via SQL*Net from client

　　2 SQL*Net roundtrips to/from client

　　0 sorts (memory)

　　0 sorts (disk)

　　10 rows processed

　　使用了FIRST_ROWS提示后，Oracle不需要扫描全表，而且避免了排序操作。

　　下面讨论最后一种情况，排序列不是索引列。这个时候排序不可避免，但是利用给出分页格式，Oracle不会对所有数据进行排序，而是只排序前N条记录。

　　SQL> SELECT OBJECT_ID, OBJECT_NAME

　　2 FROM

　　3 (

　　4 SELECT ROWNUM RN, OBJECT_ID, OBJECT_NAME

　　5 FROM

　　6 (

　　7 SELECT OBJECT_ID, OBJECT_NAME FROM T ORDER BY TIMESTAMP

　　8 )

　　9 )

　　10 WHERE RN BETWEEN 11 AND 20;

　　已选择10行。

　　Execution Plan

　　----------------------------------------------------------

　　0 SELECT STATEMENT Optimizer=CHOOSE (Cost=64 Card=6361 Bytes=585212)

　　1 0 VIEW (Cost=64 Card=6361 Bytes=585212)

　　2 1 COUNT

　　3 2 VIEW (Cost=64 Card=6361 Bytes=502519)

　　4 3 SORT (ORDER BY) (Cost=64 Card=6361 Bytes=260801)

　　5 4 TABLE ACCESS (FULL) OF 'T' (Cost=9 Card=6361 Bytes=260801)

　　Statistics

　　----------------------------------------------------------

　　0 recursive calls

　　0 db block gets

　　81 consistent gets

　　0 physical reads

　　0 redo size

　　690 bytes sent via SQL*Net to client

　　503 bytes received via SQL*Net from client

　　2 SQL*Net roundtrips to/from client

　　1 sorts (memory)

　　0 sorts (disk)

　　10 rows processed

　　SQL> SELECT OBJECT_ID, OBJECT_NAME

　　2 FROM

　　3 (

　　4 SELECT ROWNUM RN, OBJECT_ID, OBJECT_NAME

　　5 FROM

　　6 (

　　7 SELECT OBJECT_ID, OBJECT_NAME FROM T ORDER BY TIMESTAMP

　　8 )

　　9 WHERE ROWNUM <= 20

　　10 )

　　11 WHERE RN >= 11;

　　已选择10行。

　　Execution Plan

　　----------------------------------------------------------

　　0 SELECT STATEMENT Optimizer=CHOOSE (Cost=64 Card=20 Bytes=1840)

　　1 0 VIEW (Cost=64 Card=20 Bytes=1840)

　　2 1 COUNT (STOPKEY)

　　3 2 VIEW (Cost=64 Card=6361 Bytes=502519)

　　4 3 SORT (ORDER BY STOPKEY) (Cost=64 Card=6361 Bytes=260801)

　　5 4 TABLE ACCESS (FULL) OF 'T' (Cost=9 Card=6361 Bytes=260801)

　　Statistics

　　----------------------------------------------------------

　　0 recursive calls

　　0 db block gets

　　81 consistent gets

　　0 physical reads

　　0 redo size

　　690 bytes sent via SQL*Net to client

　　503 bytes received via SQL*Net from client

　　2 SQL*Net roundtrips to/from client

　　1 sorts (memory)

　　0 sorts (disk)

　　10 rows processed