Problem with variables in dynamic SQL/PLSQL

Question

Hi, I have a problem I am trying to solve using a very short piece of dynamic SQL/PLSQL but I am having problems getting the variable values out of the dynamic block.
I need to increment a counter which could be any one of 16 counters I am using and I want to avoid using nested IF statements.
The variable to be incremented is made up of the 'scheme', the 'contributory category' and the 'employment category' (although not every combination is valid)
The 'scheme' can be either 'no1', 'no2', 'off', 'cg' or 'amc'
The 'contributory category' can be either 'cont' or 'noncont'
The 'employment category' can be either 'ft' or 'pt'
For example the total variable name could be 'v_cg_noncont_ft_count'
I have created a variable by concatenating the various elements called v_incr_count_name which holds the name of the variable I want to increment.
I am running this within an anonymous PLSQL block so I cannot use global variables meaning that my variables are not visible within a dynamic PLSQL block.
As a result I think I will need to use bind variables with a PLSQL block or a SELECT FROM INTO SQL string
I have tried various solutions including the following PLSQL solution:
v_incr_count_name := 'v_'||v_scheme||'_'||v_cont_cat||'_'||v_emp_cat||'_count';
sql_stmt := 'BEGIN :a := :a + 1; END;';
EXECUTE IMMEDIATE sql_stmt USING v_incr_count_name;
Unfortunately I am getting the 'IN bind variable bound to an OUT position' error which I suppose makes sense as I am trying to change the value of a variable in the main PLSQL block from within the dynamic block.
Another (SQL) solution I tried was:
v_incr_count_name := 'v_'||v_scheme||'_'||v_cont_cat||'_'||v_emp_cat||'_count';
sql_stmt := 'SELECT '||v_incr_count_name||' + 1 FROM DUAL';
EXECUTE IMMEDIATE sql_stmt INTO v_return;
While this executes and returns the incremented value into v_return, I am still left unable to copy the returned value into the variable whose name is stored in v_incr_count_name
Any help appreciated
Cheers, Dan

Answer 1

this shows the syntax for the using clause
declare
a number := 1;
b number := null;
v varchar2(10) := 'A';
begin
execute immediate 'begin :v1 := :v1 + 1; end;' using in out a;
dbms_output.put_line(a);
end;
/but what you want cannot be done
SQL> declare
  2  a number := 1;
  3  b number := null;
  4  v varchar2(10) := 'A';
  5  begin
  6  execute immediate 'begin '||v||' := :v1 + 1; end;' using in out a;
  7  dbms_output.put_line(a);
  8  end;
  9  /
declare
ERROR at line 1:
ORA-06550: line 1, column 7:
PLS-00201: identifier 'A' must be declared
ORA-06550: line 1, column 7:
PL/SQL: Statement ignored
ORA-06512: at line 6the variable "V" contains the name of the desired output variable ("A"). this errors because "A" is not defined within the scope of the dynamic sql.
"into the variable whose name is stored in v_incr_count_name"
pl/sql does not support dereferencing variables, so you can't do it.