SQL & PL/SQL

Hi Experts,

I have the below scenario:

drop table table_x;

/

create table table_x(col1)

as

select 'A' from dual

union all

select 'B' from dual

union all

select 'C' from dual

union all

select 'D' from dual;

/

Input: A number say 1,2,3...n where n is no of elements in the table_x and can reach up to count(table_x.col1)

Output:

Case 1:

                Input: 1

                Output:                    A

                                                B

                                                C

                                                D

Case 2:

                Input: 2

                Output:                    AB

                                                AC

                                                AD

                                                BA

                                                BC

                                                BD

                                                CA

                                                CB

                                                CD

                                                DA

                                                DB

                                                DC

Logic:

The query should be able to produce the permutations whenever the user provides the number like above.

My attempt:

SELECT val

FROM   (SELECT Ltrim(Sys_connect_by_path(col1, ' '), ' ') AS VAL, LEVEL LV

             FROM   (SELECT col1,ROWID RD FROM table_x)

             CONNECT BY LEVEL <= (SELECT Count(1) FROM table_x)

             AND PRIOR rd <> rd

             AND PRIOR Sys_guid() IS NOT NULL)

WHERE  lv = :user_provided_number;

Question:

1. Is this the right way to solve this problem ? If not, then what is ? And how ?
2. Since the query takes a considerable amount of time to produce the results, is there any better method to achieve it ?

Note:

1. Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production

Appreciate the help. Thanks in advance.