Add unique constraint only if it not exists

Question

hello racle community,
I would like to create a unique constraint (at least over two columns) on several tables via a script. Is there any way to fire the ALTER TABLE statement only when a constraint over the same columns does not exists already ? Or do I have to query the USER_CONSTRAINTS table first ?
Ikrischer

Answer 1

Yes, something like this:
set serveroutput on
declare
  UNIQUE_CONS_EXISTS exception;
  pragma  exception_init(UNIQUE_CONS_EXISTS, -2261); 
begin
  for r in (select table_name
                  ,rownum rn
            from all_tables where ....) loop
    begin
      execute immediate 'alter table ' || r.Table_Name || ' add constraint i_' || r.rn || ' unique (col1,col2)';
      when UNIQUE_CONS_EXISTS then
        dbms_output.put_line(sqlerrm);
      end;
  end loop;
  dbms_output.put_line('Done');
end;
/The only thing to bear in mind is that your constraint names will simply be numbered increments and will have no meaning.