Oracle之利用函数索引减少递归调用

drop table t1 purge;

drop table t2 purge;

create table t1 (first_name varchar2(200),last_name varchar2(200),id number);                    

create table t2 as select * from dba_objects where rownum<=1000;                                 

insert into t1 (first_name,last_name,id) select object_name,object_type,rownum from dba_objects where rownum<=1000;                                    

commit;                                                                               

create or replace function get_obj_name(p_id t2.object_id%type) return t2.object_name%type DETERMINISTIC is

v_name t2.object_name%type;
begin

select object_name

into v_name

from t2

where object_id=p_id;

return v_name;

end;

/     

                                     

set linesize 1000

set autotrace traceonly   

select *  

from t1 where get_obj_name(id)='TEST'  ;

执行计划

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

| Id  | Operation         | Name | Rows  | Bytes | Cost (%CPU)| Time     |

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

|   0 | SELECT STATEMENT  |      |    10 |  2170 |     3   (0)| 00:00:01 |

|*  1 |  TABLE ACCESS FULL| T1   |    10 |  2170 |     3   (0)| 00:00:01 |

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

统计信息

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

       1057  recursive calls

          0  db block gets

      16007  consistent gets

          0  physical reads

          0  redo size

        410  bytes sent via SQL*Net to client

        404  bytes received via SQL*Net from client

          1  SQL*Net roundtrips to/from client

          0  sorts (memory)

          0  sorts (disk)

          0  rows processed

create index idx_func_id on t1(get_obj_name(id));

执行计划

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

Plan hash value: 4083325411

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

| Id  | Operation                   | Name        | Rows  | Bytes | Cost (%CPU)| Time     |

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

|   0 | SELECT STATEMENT            |             |    10 | 22190 |     2   (0)| 00:00:01 |

|   1 |  TABLE ACCESS BY INDEX ROWID| T1          |    10 | 22190 |     2   (0)| 00:00:01 |

|*  2 |   INDEX RANGE SCAN          | IDX_FUNC_ID |     4 |       |     1   (0)| 00:00:01 |

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

统计信息

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

          0  recursive calls

          0  db block gets

          2  consistent gets

          0  physical reads

          0  redo size

        410  bytes sent via SQL*Net to client

        404  bytes received via SQL*Net from client

          1  SQL*Net roundtrips to/from client

          0  sorts (memory)

          0  sorts (disk)

          0  rows processed

解析：建函数索引以后，通过执行计划发现，1057  recursive calls递归调用没有了，

由于函数索引特性会预计算所以递归调用没有了。