Add temp column with default as trim of an existing column in Oracle SQL -

i trying add temporary column table in order fix leading , trailing spaces in original column.

original column values (excluding speech marks):

" john smith   " "  jay morgan  " 

temporary column values (excluding speech marks):

"john smith" "jay morgan" 

sql:

alter table persons add t_full_name default trim(full_name); 

however, not work. trying impossible?

this worked me (oracle 11g):

create table t2 (full_name varchar2(40)); insert t2 (full_name) values ('  test  '); select * t2; alter table t2 add (fu2 varchar2(40) (trim(full_name))); select * t2; 

output

full_name   fu2   test      test 

added after comment. if later want rename columns told, can following:

alter table t2 add fu3 varchar2(40); update t2 set fu3=fu2; alter table t2 drop column fu2; alter table t2 drop column full_name; alter table t2 rename column fu3 full_name; 

or directly, if don't want intermediate checks:

update t2 set full_name=fu2; alter table t2 drop column fu2;