Oracle PL/SQL - Dereference a string as a variable - oracle

Question

Is it possible to dereference a string as a variable in PL/SQL?
I'm looking for something like this:
declare
my_var CONSTANT varchar2(50) := 'test';
my_var_ref CONSTANT varchar2(50) := 'my_var';
begin
-- This of course doesn't work, it's just to illustrate what I'm looking for:
DBMS_OUTPUT.PUT_LINE(&my_var_ref) -- Prints test
end;
Pass the name as a procedure parameter:
declare
my_var CONSTANT varchar2(50) := 'test';
my_var_ref CONSTANT varchar2(50) := 'my_var';
begin
my_func(&my_var_ref) -- Pass my_var instead of my_var_ref
end;

Answer 1

[TL;DR] No, you cannot dereference a PL/SQL variable. However, an alternative option might be to use an associative array.
If you try to dereference it using EXECUTE IMMEDIATE then the PL/SQL block that is being dynamically evaluated has no knowledge of the context from the calling block so cannot get the value of the dereferenced variable.
For example:
DECLARE
my_var CONSTANT varchar2(50) := 'test';
my_var_ref CONSTANT varchar2(50) := 'my_var';
value VARCHAR2(50);
plsql_block VARCHAR2(100) := 'BEGIN :value := ' || my_var_ref || '; END;';
BEGIN
DBMS_OUTPUT.PUT_LINE( plsql_block );
EXECUTE IMMEDIATE plsql_block USING IN OUT value;
DBMS_OUTPUT.PUT_LINE( value );
EXCEPTION
WHEN OTHERS THEN
DBMS_OUTPUT.PUT_LINE( SQLERRM );
END;
/
Outputs:
BEGIN :value := my_var; END;
ORA-06550: line 1, column 17:
PLS-00201: identifier 'MY_VAR' must be declared
It has got the correct variable name but the variable is not defined in the context within which the dynamic evaluation of the PL/SQL block is occurring so it doesn't work.
However, if you try to pass in the variable's value (rather than trying to dereference the variable) then this demonstrates that, apart from dereferencing, the rest of the code would work:
DECLARE
my_var CONSTANT varchar2(50) := 'test';
my_var_ref CONSTANT varchar2(50) := 'my_var';
value VARCHAR2(50);
plsql_block VARCHAR2(100) := 'BEGIN :value := ''' || my_var || '''; END;';
BEGIN
DBMS_OUTPUT.PUT_LINE( plsql_block );
EXECUTE IMMEDIATE plsql_block USING IN OUT value;
DBMS_OUTPUT.PUT_LINE( value );
EXCEPTION
WHEN OTHERS THEN
DBMS_OUTPUT.PUT_LINE( SQLERRM );
END;
/
Outputs:
BEGIN :value := 'test'; END;
test
However, you could use a PL/SQL associative array instead:
DECLARE
TYPE MAP IS TABLE OF VARCHAR2(50) INDEX BY VARCHAR2(50);
my_var_ref CONSTANT VARCHAR2(50) := 'my_var';
v_map MAP;
BEGIN
v_map('my_var') := 'test';
DBMS_OUTPUT.PUT_LINE( v_map( my_var_ref) );
END;
/
Which outputs:
test
db<>fiddle here

Answer 2

You can using packages.
create or replace package test_pkg as
my_var1 varchar2(50);
my_var2 varchar2(50);
my_var3 varchar2(50);
procedure set_val(p_var in varchar2,
p_val in varchar2);
function get_val(p_var in varchar2)
return varchar2;
end test_pkg;
/
create or replace package body test_pkg as
procedure set_val(p_var in varchar2,
p_val in varchar2) is
begin
execute immediate 'begin
test_pkg.' || p_var || ' := :x;
end;'
using p_val;
end set_val;
function get_val(p_var in varchar2)
return varchar2 is
v_value varchar2(50);
begin
execute immediate 'begin
:x := test_pkg.' || p_var || ';
end;'
using out v_value;
return v_value;
end get_val;
end test_pkg;
/
Then
set serveroutput on
begin
for i in 1 .. 3 loop
test_pkg.set_val('my_var' || i, 'Test ' || i);
end loop;
for i in 1 .. 3 loop
dbms_output.put_line('my_var' || i || ' = ' || test_pkg.get_val('my_var' || i));
end loop;
end;
Output:
my_var1 = Test 1
my_var2 = Test 2
my_var3 = Test 3