generating multiple columns from dual table - sql

Question

I need to generate multiple columns from dual table. Number of columns to be generated gets decided by user input. If input is 3 then three times 'ABC'. If it is 4 then 4 times 'ABC' should be selected from dual.
I tried union all but I am trying to find out more efficient way of doing it.
DECLARE
v_value varchar2(10):='ABC'
v_count number:=3;
VAR varchar2(4000)
BEGIN
select 'ABC','ABC','ABC' INTO VAR FROM DUAL;
END;

Answer 1

Try this. Here you can input the number of times 'ABC' needed as column at runtime:
Code:
declare
user_input number := #
var varchar2(10) := '''ABC''';
var1 varchar2(2000);
v_sql varchar2(1000);
v_res varchar2(4000);
begin
var1 := var;
for i in 1 .. user_input - 1 loop
var1 := var1 || ',' || var;
end loop;
var1 := LTRIM(RTRIM(var1, ','), ',');
--dbms_output.put_line(var1);
v_sql := 'select :var1 from dual';
--dbms_output.put_line(v_sql);
Execute immediate v_sql
into v_res
using var1;
dbms_output.put_line(v_res);
end;
Demo:
SQL> declare
2
3 user_input number := #
4
5 var varchar2(10) := '''ABC''';
6 var1 varchar2(2000);
7 v_sql varchar2(1000);
8 v_res varchar2(4000);
9 begin
10
11 var1 := var;
12
13 for i in 1 .. user_input - 1 loop
14 var1 := var1 || ',' || var;
15 end loop;
16
17 var1 := LTRIM(RTRIM(var1, ','), ',');
18
19 --dbms_output.put_line(var1);
20
21 v_sql := 'select :var1 from dual';
22
23 --dbms_output.put_line(v_sql);
24
25 Execute immediate v_sql
26 into v_res
27 using var1;
28
29 dbms_output.put_line(v_res);
30
31 end;
32 /
Enter value for num: 2
old 3: user_input number := #
new 3: user_input number := 2;
'ABC','ABC'
PL/SQL procedure successfully completed.
SQL> /
Enter value for num: 5
old 3: user_input number := #
new 3: user_input number := 5;
'ABC','ABC','ABC','ABC','ABC'
PL/SQL procedure successfully completed.
SQL> /
Enter value for num: 7
old 3: user_input number := #
new 3: user_input number := 7;
'ABC','ABC','ABC','ABC','ABC','ABC','ABC'
PL/SQL procedure successfully completed.
SQL> /
Enter value for num: 6
old 3: user_input number := #
new 3: user_input number := 6;
'ABC','ABC','ABC','ABC','ABC','ABC'
PL/SQL procedure successfully completed.
SQL> /
Enter value for num: 9
old 3: user_input number := #
new 3: user_input number := 9;
'ABC','ABC','ABC','ABC','ABC','ABC','ABC','ABC','ABC'
PL/SQL procedure successfully completed.

Answer 2

Is that what you mean?
select RPAD('ABC',length('ABC')*3,'ABC') from dual
ABCABCABC
DECLARE
v_value varchar2(10):='ABC'
v_count number:=3;
VAR varchar2(4000)
BEGIN
select RPAD(v_value,length(v_value)*v_count,v_value) INTO VAR FROM DUAL;
END;

Answer 3

Your question is not that clear.
The fact that you are using a VARCHAR2(4000) variable for your result value makes me think that you need to get a single string composed by the concatenation of a string n times; if this is the case, you don't need a select ... from DUAL and can simply do:
DECLARE
v_value varchar2(10):='ABC';
v_count number:=4;
VAR varchar2(4000);
BEGIN
VAR := rpad(v_value, length(v_value) * v_count, v_value);
dbms_output.put_line(VAR);
END;
/
ABCABCABCABC
But you say you tried UNION, and this makes me think you need to get n rows with the same value; in this case, you may try:
DECLARE
type yourResultType is table of varchar2(10);
v_value varchar2(10):='ABC';
v_count number:=4;
VAR yourResultType;
BEGIN
select v_value
bulk collect into VAR
from dual
connect by level <= v_count;
--
for i in VAR.first .. VAR.last loop
dbms_output.put_line(VAR(i));
end loop;
END;
/
ABC
ABC
ABC
ABC