--没有索引时一样]SQL> select count(*) from testa;
Execution Plan
----------------------------------------------------------
0 SELECT STATEMENT Optimizer=CHOOSE
1 0 SORT (AGGREGATE)
2 1 TABLE ACCESS (FULL) OF 'TESTA'
Statistics
----------------------------------------------------------
103 recursive calls
5 db block gets
10 consistent gets
5 physical reads
0 redo size
152 bytes sent via SQL*Net to client
308 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
2 sorts (memory)
0 sorts (disk)
1 rows processedSQL> select count(*) from (select * from testa);
Execution Plan
----------------------------------------------------------
0 SELECT STATEMENT Optimizer=CHOOSE
1 0 SORT (AGGREGATE)
2 1 TABLE ACCESS (FULL) OF 'TESTA'
Statistics
----------------------------------------------------------
0 recursive calls
4 db block gets
1 consistent gets
2 physical reads
0 redo size
169 bytes sent via SQL*Net to client
308 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
1 rows processedSQL>
Execution Plan
----------------------------------------------------------
0 SELECT STATEMENT Optimizer=CHOOSE
1 0 SORT (AGGREGATE)
2 1 TABLE ACCESS (FULL) OF 'TESTA'
Statistics
----------------------------------------------------------
103 recursive calls
5 db block gets
10 consistent gets
5 physical reads
0 redo size
152 bytes sent via SQL*Net to client
308 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
2 sorts (memory)
0 sorts (disk)
1 rows processedSQL> select count(*) from (select * from testa);
Execution Plan
----------------------------------------------------------
0 SELECT STATEMENT Optimizer=CHOOSE
1 0 SORT (AGGREGATE)
2 1 TABLE ACCESS (FULL) OF 'TESTA'
Statistics
----------------------------------------------------------
0 recursive calls
4 db block gets
1 consistent gets
2 physical reads
0 redo size
169 bytes sent via SQL*Net to client
308 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
1 rows processedSQL>
Execution Plan
----------------------------------------------------------
0 SELECT STATEMENT Optimizer=CHOOSE (Cost=1 Card=1)
1 0 SORT (AGGREGATE)
2 1 INDEX (FULL SCAN) OF 'FND_USER_U1' (UNIQUE) (Cost=1 Card
=450)Statistics
----------------------------------------------------------
0 recursive calls
0 db block gets
1 consistent gets
0 physical reads
0 redo size
170 bytes sent via SQL*Net to client
308 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
1 sorts (memory)
0 sorts (disk)
1 rows processedSQL> select count(*) from (select * from fnd_user );
Execution Plan
----------------------------------------------------------
0 SELECT STATEMENT Optimizer=CHOOSE (Cost=1 Card=1)
1 0 SORT (AGGREGATE)
2 1 INDEX (FULL SCAN) OF 'FND_USER_U1' (UNIQUE) (Cost=1 Card
=450)Statistics
----------------------------------------------------------
381 recursive calls
3 db block gets
62 consistent gets
12 physical reads
0 redo size
170 bytes sent via SQL*Net to client
308 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
14 sorts (memory)
0 sorts (disk)
1 rows processedSQL>
自己在taod 里测试了一下
有点不大清楚