SQL> drop table T1 purge;

Table dropped.

SQL>
SQL> create table t1 ( userid int, cityid varchar2(10));

Table created.

SQL>
SQL> insert into t1 values (101 ,'BLR');

1 row created.

SQL> insert into t1 values (104 ,'CTC');

1 row created.

SQL> insert into t1 values (103 ,'DEL');

1 row created.

SQL> insert into t1 values (104 ,'BLR');

1 row created.

SQL> insert into t1 values (105 ,'NSK');

1 row created.

SQL> insert into t1 values (101 ,'CTC');

1 row created.

SQL> insert into t1 values (103 ,'BLR');

1 row created.

SQL>
SQL> create or replace
  2  procedure list_users(p_cities sys.odcivarchar2list) is
  3  begin
  4    for i in (
  5      select *
  6      from   t1
  7      where  cityid in ( select column_value from table(p_cities))
  8      )
  9    loop
 10      dbms_output.put_line(i.userid||','||i.cityid);
 11    end loop;
 12  end;
 13  /

Procedure created.

SQL>
SQL> set serverout on
SQL> exec list_users(sys.odcivarchar2list('BLR'));
103,BLR
104,BLR
101,BLR

PL/SQL procedure successfully completed.

SQL> exec list_users(sys.odcivarchar2list('BLR','DEL'));
103,BLR
104,BLR
101,BLR
103,DEL

PL/SQL procedure successfully completed.

SQL>
SQL>
SQL>