SQL & PL/SQL

I make a “Create Table as” and I receive the error ORA-01723: zero-length columns are not allowed because I make:

create table TABLE1 as (select field1, fields2, ‘’ my_field3, ‘’ my_field4 from XXX)

I need “my_field3” VARCHAR2(25) and “my_field4” NUMBER(12)


How can I do the “Create table as”???????