Question

Sorry about the rubbish question title. I have a table SET_DEFINITIONS like this:

SETKEY      NOT NULL    NUMBER(38)
SETENTRY    NOT NULL    NUMBER(38)

where the idea is that the rows define sets of numbers. For example the table could contain rows:

1 2
1 4
2 1
2 2

which would mean set 1 is {2,4} and set 2 is {1,2}. I want to write a function

function selectOrInsertSet(table of number(38) numbers) return number(38)

which will return the key of a set with the same members as the passed in table (or create such a set if it doesn’t exist). What’s a good way to do this in PL/SQL?

EDIT: the solution I’m currently working on goes like this (and I’m not sure it’ll work):

1. select all keys that have the first element into some collection c
2. refine the collection c by intersecting with successive sets of keys that contain the other elements

Answer 1

You can use a full outer join between each set and the collection of numbers to see if they are the same. This function does that:

function selectOrInsertSet(numbers number_tt) return number
is
  l_diff number;
  l_retval number;
begin
  for r in (select distinct setkey from set_definitions)
  loop
     with d as (select column_value from table(numbers)),
          s as (select setentry from set_definitions where setkey=r.setkey)
     select count(*)
     into   l_diff
     from   s
     full outer join d on d.column_value = s.setentry
     where s.setentry is null or d.column_value is null;

     if l_diff = 0 then
        l_retval := r.setkey;
        exit;
     end if;
  end loop;

  return l_retval;
end;

This returns the setkey if found, else null.

I haven’t implemented the part about creating a new set if none is found, but that should be easy enough. I don’t personally like functions that have side effects (in this case, inserting rows into a table).