Example of EXECUTE IMMEDIATE usage

1. To run a DDL statement in PL/SQL.
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begin
execute immediate 'set role all';
end;


2. To pass values to a dynamic statement (USING clause).
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declare
l_depnam varchar2(20) := 'testing';
l_loc varchar2(10) := 'Dubai';
begin
execute immediate 'insert into dept values (:1, :2, :3)'
using 50, l_depnam, l_loc;
commit;
end;


3. To retrieve values from a dynamic statement (INTO clause).
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declare
l_cnt varchar2(20);
begin
execute immediate 'select count(1) from emp'
into l_cnt;
dbms_output.put_line(l_cnt);
end;


4. To call a routine dynamically: The bind variables used for parameters of the routine have to be specified along with the parameter type. IN type is the default, others have to be specified explicitly.
------------------------------------------------------------------

declare
l_routin varchar2(100) := 'gen2161.get_rowcnt';
l_tblnam varchar2(20) := 'emp';
l_cnt number;
l_status varchar2(200);
begin
execute immediate 'begin ' || l_routin || '(:2, :3, :4); end;'
using in l_tblnam, out l_cnt, in out l_status;

if l_status != 'OK' then
dbms_output.put_line('error');
end if;
end;


5. To return value into a PL/SQL record type: The same option can be used for %rowtype variables also.
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declare
type empdtlrec is record (empno number(4),
ename varchar2(20),
deptno number(2));
empdtl empdtlrec;
begin
execute immediate 'select empno, ename, deptno ' ||
'from emp where empno = 7934'
into empdtl;
end;


6. To pass and retrieve values: The INTO clause should precede the USING clause.
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declare
l_dept pls_integer := 20;
l_nam varchar2(20);
l_loc varchar2(20);
begin
execute immediate 'select dname, loc from dept where deptno = :1'
into l_nam, l_loc
using l_dept ;
end;


7. Multi-row query option. Use the insert statement to populate a temp table for this option. Use the temporary table to carry out further processing. Alternatively, you may use REF cursors to by-pass this drawback.
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declare
l_sal pls_integer := 2000;
begin
execute immediate 'insert into temp(empno, ename) ' ||
' select empno, ename from emp ' ||
' where sal > :1'
using l_sal;
commit;
end;



EXECUTE IMMEDIATE is a much easier and more efficient method of processing dynamic statements than could have been possible before. As the intention is to execute dynamic statements, proper handling of exceptions becomes all the more important. Care should be taken to trap all possible exceptions.

for details
http://docs.oracle.com/cd/B14117_01/appdev.101/b10807/13_elems017.htm