About the original question :

Do not forget to fill the table with data before you create the MV.

Example

create materialized view T_MV
...
as select id,sum(amount) as s_a
from sales
group by id

equals

create table T_MV
as select is,sum(amount) as s_a
from sales
group by id
/
create materialized view T_MV on prebuilt table
...
as select id,sum(amount) as s_a
from sales
group by id
/

Limitation :
The table you use must have the same name as the MV.

Wrong example

create table T_MV ( id number, s_a number )
/
create materialized view T_MV on prebuilt table
...
as select id,sum(amount) as s_a
from sales
group by id
/

remark

If the materialized view is dropped, the preexisting table reverts to its identity as a table.



Hope this helps
Gert