Oracle function return table - sql

Question

I don't know what is best solution for my problem. I need function with one parameter which resault is
VAL
-----
1
2
3
In function I need put union all to get all value.
Select column_1 as VAL from my_table where id = P_FUNCTION_PARAMETER --return 1
union all
Select column_2 as VAL from my_table where id = P_FUNCTION_PARAMETER --return 2
union all
Select column_3 as VAL from my_table where id = P_FUNCTION_PARAMETER; --return 3
What is the best solution for this?

Answer 1

"Best" just depends. Return a ref cursor or a collection, whichever you prefer.
For example:
SQL> create or replace function f_test_rc
2 return sys_refcursor
3 is
4 rc sys_refcursor;
5 begin
6 open rc for
7 select 1 from dual union all
8 select 2 from dual union all
9 select 3 from dual;
10
11 return rc;
12 end;
13 /
Function created.
SQL> select f_test_rc from dual;
F_TEST_RC
--------------------
CURSOR STATEMENT : 1
CURSOR STATEMENT : 1
1
----------
1
2
3
SQL> create or replace function f_test_coll
2 return sys.odcinumberlist
3 as
4 l_coll sys.odcinumberlist;
5 begin
6 select * bulk collect into l_coll
7 from (select 1 from dual union all
8 select 2 from dual union all
9 select 3 from dual
10 );
11
12 return l_coll;
13 end;
14 /
Function created.
SQL> select * from table(f_test_coll);
COLUMN_VALUE
------------
1
2
3
SQL>

Answer 2

First let's set up a small table for testing:
create table my_table
( id number primary key
, column_1 number
, column_2 number
, column_3 number
);
insert into my_table
select 1008, 3, -8, 0.2 from dual union all
select 1002, 6, null, -1.2 from dual
;
commit;
The function can look like this. Note that I don't use union all - that will require reading the table three times, when only one time is enough.
create or replace function my_function (p_function_parameter number)
return sys.odcinumberlist
as
arr sys.odcinumberlist;
begin
select case ord when 1 then column_1
when 2 then column_2
when 3 then column_3 end
bulk collect into arr
from my_table cross join
(select level as ord from dual connect by level <= 3)
where id = p_function_parameter
order by ord
;
return arr;
end;
/
The function could be used, for example, like this: (in older versions you may need to wrap the function call within the table operator)
select * from my_function(1002);
COLUMN_VALUE
------------
6
-1.2