Print a json structure from a dynamic query - sql

Question

I want to create function that return a CLOB with a json content.
But first i want to print the result (see query code) to see how it looks like.
The result must be a json, that will contain the information for 1 record just, this record select query, must be created dynamically.
So I try the next query, to resolve this problem. but i get an error.
Query
declare
v_stmt VARCHAR2(1000);
l_sep varchar2(1) := chr(10);
l_tab varchar2(1) := chr(9);
up_column VARCHAR2(50);
low_column VARCHAR2(50);
cur_asc SYS_REFCURSOR;
Vcdogcur SYS_REFCURSOR;
id_ccd number;
first boolean := true;
begin
id_ccd := 174;
v_stmt := 'select ';
open cur_asc for
SELECT column_name as up_column
,lower(column_name) as low_column
FROM USER_TAB_COLUMNS
WHERE table_name = upper('my_table');
loop
FETCH cur_asc
INTO up_column, low_column;
EXIT WHEN cur_asc%NOTFOUND;
if not first then
v_stmt := v_stmt || ',';
end if;
first := false;
v_stmt := v_stmt || l_sep || l_tab ||up_column || ' as ' || low_column;
END LOOP;
--v_stmt := v_stmt || l_sep || 'from my_table' || l_sep ||'where id = ' || id_ccd || ';';
v_stmt := v_stmt || l_sep || 'from my_table' || l_sep ||'where id = ' || id_ccd;
DBMS_OUTPUT.PUT_LINE('salida: ' || v_stmt);
CLOSE cur_asc;
--v_stmt := v_stmt || l_sep || 'from my_table' || l_sep ||'where id = ' || id_ccd;
--DBMS_OUTPUT.PUT_LINE('salida: ' || v_stmt);
open Vcdogcur for v_stmt;
APEX_JSON.initialize_clob_output;
APEX_JSON.open_object;
APEX_JSON.write('my_table', Vcdogcur);
APEX_JSON.close_object;
DBMS_OUTPUT.put_line(APEX_JSON.get_clob_output);
CLOSE Vcdogcur;
end;
/
DBMS output
salida: select
CREATED as created,
CREATED_BY as created_by,
UPDATED as updated,
UPDATED_BY as updated_by,
ID as id,
TEXT as text,
PART as part,
CODE as code,
DATE as date,
PERCENTAGE as percentage
from my_table
where id = 174
{
"my_table":[
{
"CREATED":"2020-06-04T08:10:09.000000000Z"
,"CREATED_BY":"APEX_APP"
,"UPDATED":"2020-06-04T10:10:09.295632000Z"
,"UPDATED_BY":"APEX_APP"
,"ID":174
,"TEXT":"ALL"
,"PART":2770
,"CODE":2212
,"DATE":"2017-01-01T00:00:00.000000000Z"
,"PERCENTAGE":-4.98
}
]
}
Error
Informe de error -
ORA-01001: cursor no válido
ORA-06512: en línea 44
01001. 00000 - "invalid cursor"
*Cause:
*Action:
Can somebody help me to resolve this?
Best Regards