In early Oracle releases, you could have 1 trigger per type of trigger per table (eg if you had a before-row-insert trigger, you could have only 1). Now there is no limit. So let's look at the following example:

SQL> drop table t1 purge;

Table dropped.

SQL>
SQL>
SQL> create table T1 ( x int, y int, z int );

Table created.

SQL>
SQL> create or replace
  2  trigger trg1
  3  before insert on t1
  4  for each row
  5  begin
  6    :new.y := :new.x;
  7  end;
  8  /

Trigger created.

SQL>
SQL>
SQL> create or replace
  2  trigger trg2
  3  before insert on t1
  4  for each row
  5  begin
  6    :new.z := :new.y;
  7  end;
  8  /

Trigger created.

Seems simple enough...Copy 'x' into 'y', and then copy 'y' into 'z'. So lets see what happens

SQL>
SQL> insert into t1 (x) values (1);

1 row created.

SQL>
SQL> select * from t1;

         X          Y          Z
---------- ---------- ----------
         1          1

Where did "Z" go ? What happened was TRG2 fired first, and then TRG1 fired. The order is *indeterminate*. We can use the FOLLOWS command to dictate the order in which triggers must fire.

SQL>
SQL> create or replace
  2  trigger trg2
  3  before insert on t1
  4  for each row
  5  follows trg1
  6  begin
  7    :new.z := :new.y;
  8  end;
  9  /

Trigger created.

SQL>
SQL> insert into t1 (x) values (1);

1 row created.

SQL>
SQL> select * from t1;

         X          Y          Z
---------- ---------- ----------
         1          1
         1          1          1

SQL>
SQL>

Hope this helps.