oracle中的deterministic关键字

转自：http://www.anbob.com/?p=820

　　今天学习物化视图，在Oracle9.2.0.0上遇到这个问题，但在9.2.0.8上没有这个问题。就上网查了查，又新掌握了点知识。

SQL> conn zwz
Enter password:
Connected.
SQL> desc testfun;
Name                                      Null?    Type
----------------------------------------- -------- ----------------------------
ID                                                 NUMBER(38)
NAME                                               VARCHAR2(22)

SQL> select * from testfun;

ID NAME
---------- ----------------------
1 anbob.com
2 anbob.com
3 weijar.com

SQL> create or replace function f_upp(p_name varchar2)
2  return varchar2
3is
4begin
5return  upper(p_name);
6  end;
7  /

Function created.

SQL> create index idx_f_upp on testfun(f_upp(name));
create index idx_f_upp on testfun(f_upp(name))
*
ERROR at line 1:
ORA-30553: The function is not deterministic

SQL> create or replace function f_upp(p_name varchar2)
2  return varchar2 deterministic
3  begin
4    return upper(p_name);
5* end;

Warning: Function created with compilation errors.

SQL> show err
Errors for FUNCTION F_UPP:

LINE/COL ERROR
-------- -----------------------------------------------------------------
3/1      PLS-00103: Encountered the symbol "BEGIN" when expecting one of
the following:
; is authid as cluster order using external deterministic
parallel_enable pipelined aggregate
The symbol "is" was substituted for "BEGIN" to continue.

SQL>l2
2* return varchar2 deterministic
SQL> input is
SQL> l
1  create or replace function f_upp(p_name varchar2)
2  return varchar2 deterministic
3  is
4  begin
5    return upper(p_name);
6* end;
SQL> run
1  create or replace function f_upp(p_name varchar2)
2  return varchar2 deterministic
3  is
4  begin
5    return upper(p_name);
6* end;

Function created.

SQL> create index idx_f_upp on testfun(f_upp(name));

Index created..
Specify DETERMINISTIC to indicate that the function returns the same result value whenever it is called with the same values for its arguments.

You must specify this keyword if you intend to call the function in the expression of a function-based index or from the query of a materialized view that is marked REFRESH FAST or ENABLE QUERY REWRITE. When Oracle Database encounters a deterministic function in one of these contexts, it attempts to use previously calculated results when possible rather than reexecuting the function. If you subsequently change the semantics of the function, you must manually rebuild all dependent function-based indexes and materialized views.

这个关键字表明:如果你的函数当输入一样时,会返回同样的结果.
这样, 数据库就用前一个计算的值,而不需要再重新计算一次.
这对于使用函数索引等,会得到相当大的好处.

英文说明：

DETERMINISTIC Clause

Specify DETERMINISTIC to indicate that the function returns the same result value whenever it is called with the same values for its arguments.

You must specify this keyword if you intend to call the function in the expression of a function-based index or from the query of a materialized view that is marked REFRESH FAST or ENABLE QUERY REWRITE. When Oracle Database encounters a deterministic function in one of these contexts, it attempts to use previously calculated results when possible rather than reexecuting the function. If you subsequently change the semantics of the function, you must manually rebuild all dependent function-based indexes and materialized views.

Do not specify this clause to define a function that uses package variables or that accesses the database in any way that might affect the return result of the function. The results of doing so will not be captured if Oracle Database chooses not to reexecute the function.

The following semantic rules govern the use of the DETERMINISTIC clause:

You can declare a top-level subprogram DETERMINISTIC.

You can declare a package-level subprogram DETERMINISTIC in the package specification but not in the package body.

You cannot declare DETERMINISTIC a private subprogram (declared inside another subprogram or inside a package body).

A DETERMINISTIC subprogram can call another subprogram whether the called program is declared DETERMINISTIC or not.