Query to get a combination of values

Question

I have 4 tables, say T1,T2,T3,T4.
I want to select 4 columns from this 4 tables respectively.
How can I write a query to fetch all possible combinations of these 4 columns.

Answer 1

The only way to combine columns is to write a SQL statement where you written possible combinations of these columns.
You can develop something to combine the values but you can't manipulate columns very easily.
SQL> SELECT ENUMERATIONS.PERMUTA(STRING_TABLE('A','B','C'))
  2  FROM DUAL
  3  /
ENUMERATIONS.PERMUTA(STRING_TABLE('A','B','C'))
STRING_TABLE('ABC', 'ACB', 'BAC', 'BCA', 'CAB', 'CBA')
SQL>To do it I use the following package.
CREATE OR REPLACE
TYPE string_table as table of varchar2(4000)
CREATE OR REPLACE
PACKAGE enumerations is
     type bool_tab is table of boolean index by binary_integer;
     flags bool_tab;
     solutions string_table;
     function permuta (
          strings in string_table
     ) return string_table;
end enumerations;
CREATE OR REPLACE
PACKAGE BODY enumerations is
     procedure permutations (
          i in pls_integer,
          strings in string_table,
          current_string in varchar2
     is
          n pls_integer;
          j pls_integer;
     begin
          n := cardinality(strings);
          if ( i <= n ) then
               for j in 1..n loop
                    if ( not flags(j) ) then
                         flags(j) := true;
                         permutations(i+1,strings,current_string||strings(j));
                         flags(j) := false;
                    end if;
               end loop;
          else
               solutions.extend();
               solutions(solutions.last) := current_string;
          end if;
     end;
     function permuta (
          strings in string_table
     ) return string_table
     is
     begin
          for i in 1..cardinality(strings) loop
               flags(i) := false;
          end loop;
          solutions := string_table();
          permutations(1,strings,'');
          return solutions;
     end;
end enumerations;
/Bye Alessandro