Oracle “create table as” with null column value

When creating new tables with from a query output you may use "create table as" statement.

Sometimes you need to specify hardcoded null values for some columns. For example, in the following query we want null value for col_3:

create table NewTable as 
select 
   col_1, 
   col_2, 
   null col_3
from OldTable;

If you create an Oracle table using "create as" where one of your fields is null you will get the error:

ORA-01723: zero-length columns are not allowed

To fix this issue, you can cast the null value to a target data type and specify the size of the field where required. For example:

create table NewTable as 
select 
   col_1,
   col_2,
   cast(null as varchar2(100)) col_3,
   cast(null as date) col_4,
   cast(null as number) col_5
from OldTable;