sql>create table t (p varchar2(32));
 
Table created.
 
sql>create or replace trigger t_trg
  2  after insert on t
  3  for each row
  4  begin
  5    if    instr(:new.p, '/') = 0
  6       or length(replace(substr(:new.p, 3, 3), '/')) <> 2
  7       or instr(substr(:new.p, 1, 2) || substr(:new.p, 6), '/') > 0 then
  8      
  9      raise_application_error(-20000, 'Invalid phone number (' || :new.p || ')');
 10      
 11    end if;
 12  end;
 13  /
 
Trigger created.
 
sql>insert into t values ('99/9999999');
1 row created.
 
sql>insert into t values ('999/999999');
1 row created.
 
sql>insert into t values ('9999/999999');
1 row created.
 
sql>insert into t values ('9/999999999');
insert into t values ('9/999999999')
            *
ERROR at line 1:
ORA-20000: Invalid phone number (9/999999999)
ORA-06512: at "T_TRG", line 6
ORA-04088: error during execution of trigger 'T_TRG'
 
sql>insert into t values ('9999999999');
insert into t values ('9999999999')
            *
ERROR at line 1:
ORA-20000: Invalid phone number (9999999999)
ORA-06512: at "T_TRG", line 6
ORA-04088: error during execution of trigger 'T_TRG'
 
sql>insert into t values ('99//99999999');
insert into t values ('99//99999999')
            *
ERROR at line 1:
ORA-20000: Invalid phone number (99//99999999)
ORA-06512: at "T_TRG", line 6
ORA-04088: error during execution of trigger 'T_TRG'