How to use sets in PL/SQL

Question

Hi all,
I want to know how to implement algebraic sets in PL/SQl.
I mean for example if there is a table R(A,B) where A is aprimary key having the data :-
{(1,2),(2,1),(2,3),(3,1)}
i want to have a data type that represents sets of data corresponding to attribute B.
i.e the data type should have the value {1,2,3}
Thanks.

Answer 1

Not sure that I understand correctly.. and how you want to fit PL/SQL into this.
Sets are best handles as Oracle tables. The best language to deal with sets are SQL. So to get the results you want should be a simple:
SELECT DISTINCT b FROM table_r ORDER BY 1
The results of this can be a cursor that needs to be stepped (fetch) through.
The results can be bulk collected into a dynamic array, e.g.
create or replace type TArray is table of number;
And then in PL/SQL:declare
  array TArray;
begin
  SELECT DISTINCT b BULK COLLECT INTO array FROM table_r ORDER BY 1;
end;The array object will now contain TArray(1,2,3).