SQL> l
  1  declare
  2    l_ename emp.ename%type;
  3  begin
  4    select ename into l_ename
  5    from emp;
  6  exception
  7    when too_many_rows_found then               --> WRONG!
  8      dbms_output.put_line('Too many rows');
  9* end;
SQL> /
  when too_many_rows_found then
       *
ERROR at line 7:
ORA-06550: line 7, column 8:
PLS-00201: identifier 'TOO_MANY_ROWS_FOUND' must be declared
ORA-06550: line 0, column 0:
PL/SQL: Compilation unit analysis terminated


SQL>

SQL> l7
  7*   when too_many_rows_found then
SQL> c/_found//
  7*   when too_many_rows then
SQL> l
  1  declare
  2    l_ename emp.ename%type;
  3  begin
  4    select ename into l_ename
  5    from emp;
  6  exception
  7    when too_many_rows then                     --> CORRECT!
  8      dbms_output.put_line('Too many rows');
  9* end;
SQL> /
Too many rows

PL/SQL procedure successfully completed.

SQL>