How to fetch rows using exec_sql

Question

hello to all
i want to open a cursor and fetch some field values dynamically."the fields to be fetched will be selected by the user" i.e i have to get the data of the fields selected by the user.
for this i am using the exec_sql method.
its giving a message as 'FRM-01747: invalid user.table.column,table.column or column specification"
i don't where i am wrong in the code.
this is my code to fetch the values
Declare
     Con_id EXEC_SQL.CONNTYPE;
     Cur_id EXEC_SQL.CURSTYPE;
     sqlstr varchar2(3000);
     fld1 number(20,2);
     fld2 number(20,2);
     fld3 number(20,2);
     fld4 number(20,2);
     fld5 number(20,2);
     fld6 number(20,2);
     fld7 number(20,2);
     fld8 number(20,2);
     nEmpno number(10,4);
     nIgn PLS_INTEGER;
     totRows number(5);
     a number;
Begin
--1
Con_id := EXEC_SQL.DEFAULT_CONNECTION;--('scott/tiger@siil');
go_block('BlkDet');
Cur_id := EXEC_SQL.OPEN_CURSOR();
sqlstr := 'Select A.EmpNo,A.'||:BlkMain.LstFld1||',A.';
sqlstr := sqlstr||:BlkMain.LstFld2||',A.';
sqlstr := sqlstr||:BlkMain.LstFld3||',A.';
sqlstr := sqlstr||:BlkMain.LstFld4||',B.';
sqlstr := sqlstr||:BlkMain.LstFld1||',B.';
sqlstr := sqlstr||:BlkMain.LstFld2||',B.';
sqlstr := sqlstr||:BlkMain.LstFld3||',B.';
sqlstr := sqlstr||:BlkMain.LstFld4;
sqlstr := sqlstr||' from Tempsalmast A, SalMast B';
sqlstr := SqlStr||' where A.EmpNo=B.EmpNo';
Message(SqlStr);
Message(SqlStr);
EXEC_SQL.DEFINE_COLUMN(Con_id,Cur_id,1,nEmpNo);
EXEC_SQL.DEFINE_COLUMN(Con_id,Cur_id,2,Fld1);
EXEC_SQL.DEFINE_COLUMN(Con_id,Cur_id,3,Fld2);
EXEC_SQL.DEFINE_COLUMN(Con_id,Cur_id,4,Fld3);
EXEC_SQL.DEFINE_COLUMN(Con_id,Cur_id,5,Fld4);
EXEC_SQL.DEFINE_COLUMN(Con_id,Cur_id,6,Fld5);
EXEC_SQL.DEFINE_COLUMN(Con_id,Cur_id,7,Fld6);
EXEC_SQL.DEFINE_COLUMN(Con_id,Cur_id,8,Fld7);
EXEC_SQL.DEFINE_COLUMN(Con_id,Cur_id,9,Fld8);
EXEC_SQL.PARSE(Con_id,Cur_id,sqlstr,EXEC_SQL.V7);
nIgn:=EXEC_SQL.EXECUTE(Con_id,Cur_id);
while (EXEC_SQL.FETCH_ROWS(Con_id,Cur_id)>0) Loop
EXEC_SQL.COLUMN_VALUE(Con_id,Cur_id,1,nEmpNo);
EXEC_SQL.COLUMN_VALUE(Con_id,Cur_id,2,Fld1);
EXEC_SQL.COLUMN_VALUE(Con_id,Cur_id,3,Fld2);
EXEC_SQL.COLUMN_VALUE(Con_id,Cur_id,4,Fld3);
EXEC_SQL.COLUMN_VALUE(Con_id,Cur_id,5,Fld4);
EXEC_SQL.COLUMN_VALUE(Con_id,Cur_id,6,Fld5);
EXEC_SQL.COLUMN_VALUE(Con_id,Cur_id,7,Fld6);
EXEC_SQL.COLUMN_VALUE(Con_id,Cur_id,8,Fld7);
EXEC_SQL.COLUMN_VALUE(Con_id,Cur_id,9,Fld8);
:BlkDet.TxtEmpNo:=nEmpNo;
:BlkDet.DisFld1 :=Fld1;
:BlkDet.DisFld2 :=Fld2;
:BlkDet.DisFld3 :=Fld3;
:BlkDet.DisFld4 :=Fld4;
:BlkDet.TxtFld1 :=Fld5;
:BlkDet.TxtFld2 :=Fld6;
:BlkDet.TxtFld3 :=Fld7;
:BlkDet.TxtFld4 :=Fld8;
next_record;
end Loop;
--next_record;
end;
exception
     when others then
     Message(Dbms_Error_Text);
     Message(Dbms_Error_Text);
can any body pls. help me out
aditya

Answer 1

Fetching rows to display them is a task for the client tool. You need to define a ref cursor therefore.
If you just want to play around, here we go
SQL> DECLARE
  2    type t1 is table of emp%rowtype index by binary_integer;
  3    var1 t1;
  4    v_counter number:=0;
  5  BEGIN
  6    select * bulk collect into var1 from emp;
  7    for vr in 1..var1.count loop
  8      dbms_output.put_line(var1(vr).ename);
  9      update dept set deptno=var1.deptno Here also Error occured.
10    end loop;
11  END;
12  /
SCOTT
ADAMS
PL/SQL procedure successfully completed.
SQL>