Performance... Why a function column in a view is executed more than once...?

Question

Why a function column created inside a view is executed more than once when called more than once?
EXAMPLE:
create or replace view aux1 as
date_column,
any_function(date_column) column1
from any_table
create or replace view aux2 as
column1 c1,
column1 c2,
column1 c3
from aux1
select * from aux2
It will execute 3 times the function any_function... logically the value will be the same for all columns...
I understand why!... are 3 calls... but...
Why not to create a "small" verification and if the function column was execute replace the second, the third... value? ... instead of execute 3, 4... times...
tks
Braga

Answer 1

Actually, this is more than a performance issue. This is a consistency problem. If the function is NOT deterministic then you may get different values for each call which is clearly not consistent with selecting 3 copies of the same column from a row. Oracle appears to have fixed this in 9i...
Connected to:
Oracle8i Enterprise Edition Release 8.1.7.2.0 - Production
With the Partitioning option
JServer Release 8.1.7.2.0 - Production
create view v1 as select dbms_random.value(1,100) r from dual;
create view v2 as select r r1, r r2 from v1;
select * from v2;
          R1           R2
          93           74
Connected to:
Oracle9i Enterprise Edition Release 9.0.1.3.0 - Production
With the Partitioning option
JServer Release 9.0.1.3.0 - Production
create view v1 as select dbms_random.value(1,100) r from dual;
create view v2 as select r r1, r r2 from v1;
select * from v2;
          R1           R2
          78           78Richard