You can find the following view to access all metadata about the columns :

user_tab_cols; — For all tables owned by the user

all_tab_cols ; — For all tables accessible to the user

dba_tab_cols; — For all tables in the Database.

and lets consider you want to add new column only if doesn’t exists you can use this pl/sql to check and add new column

[code]DECLARE
v_column_exists number := 0;
BEGIN
Select count(*)
into v_column_exists
from user_tab_cols
where column_name = ‘ADD_COLUMN’
and table_name = ‘departments’;

if (v_column_exists = 0) then
execute immediate ‘alter table departments add (ADD_COLUMN NUMBER)’;
end if;
end;[/code]

hope this help.