access and filter，accessfilter

access and filter，accessfilter

access:表示這個謂詞條件的值將會影響資料的訪問路徑(表還是索引)。

filter:表示謂詞條件的值並不會影響資料訪問路徑，只起到過濾的作用。

----建立一張表echo----SQL> create table echo as select * from dba_objects;Table created.SQL> set autotrace trace exp;SQL> set linesize 150;SQL> select * from echo where object_id=1000;Execution Plan----------------------------------------------------------Plan hash value: 642657756--------------------------------------------------------------------------| Id  | Operation      | Name | Rows  | Bytes | Cost (%CPU)| Time     |--------------------------------------------------------------------------|   0 | SELECT STATEMENT  |     |    12 |  2484 |   289   (1)| 00:00:04 ||*  1 |  TABLE ACCESS FULL| ECHO |    12 |  2484 |   289   (1)| 00:00:04 |--------------------------------------------------------------------------Predicate Information (identified by operation id):---------------------------------------------------   1 - filter("OBJECT_ID"=1000)  ----因為表echo沒有建立索引，執行計畫沒有選擇資料訪問路徑的餘地，謂詞條件在這裡只是起到資料過濾的作用，所以使用了filter。Note-----   - dynamic sampling used for this statement (level=2) ----建立索引的情況----SQL> create index echo_ind on echo(object_id);Index created.SQL> select * from echo where object_id=1000;Execution Plan----------------------------------------------------------Plan hash value: 1345159126----------------------------------------------------------------------------------------| Id  | Operation            | Name     | Rows  | Bytes | Cost (%CPU)| Time     |----------------------------------------------------------------------------------------|   0 | SELECT STATEMENT        |           |     1 |   207 |     2     (0)| 00:00:01 ||   1 |  TABLE ACCESS BY INDEX ROWID| ECHO     |     1 |   207 |     2     (0)| 00:00:01 ||*  2 |   INDEX RANGE SCAN        | ECHO_IND |     1 |       |     1     (0)| 00:00:01 |----------------------------------------------------------------------------------------Predicate Information (identified by operation id):---------------------------------------------------   2 - access("OBJECT_ID"=1000)  ----謂詞條件影響到資料訪問的路徑，選擇了索引，所以用access。Note-----   - dynamic sampling used for this statement (level=2)

以上