oracle deterministic关键字

http://inthirties.com:90/viewthread.jsp?tid=1395
这个deterministic是不是很眼熟呀，
我们在online redefinition里见到过这个关键字，这个关键在在自定义的函数索引里也出现了。
先看看文档
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.
要实现自己的函数，加入函数索引，必须加入这个deterministic关键字，保证你这行的返回是一个确定数。
否则出现
30553, 00000, “The function is not deterministic”
// *Cause: The function on which the index is defined is not
deterministic
// *Action: If the function is deterministic, mark it
DETERMINIS