We are in the process of creating masked data using PL/SQL.We adapted Create as select as one of the approaches to masked the data in the target table.

Below is sample source table structure

COLUMN NAME DATATYPE
EMPID NUMBER(8)
NAME VARCHAR2(40)
DOB TIMESTAMP(6)

While creating the target table we are masking NAME and DOB columns and inputting the masked data in the target table.

Below is the target table structure after masking

COLUMN NAME DATATYPE
EMPID NUMBER(8)
NAME VARCHAR2(100)
DOB DATE


Please help us understand why there is a difference in the source and target table structure using masking for Create As select .

create table t_copy as 
  select cast ( c1 as ... ) c1 ,
         cast ( c2 as ... ) c2 ,
         ...
  from   t;