MODIFY COLUMN in oracle - How to check if a column is nullable before setting to nullable?

Answer

You could do this in PL/SQL:

declare
  l_nullable varchar2(1);
begin
  select nullable into l_nullable
  from user_tab_columns
  where table_name = 'MYTABLE'
  and   column_name = 'MYCOLUMN';

  if l_nullable = 'N' then
    execute immediate 'alter table mytable modify (mycolumn null)';
  end if;
end;