How do i insert into table through forms

Question

Hi
I have developed a custom form based on custom table.
the only way to insert data into database table is through form.
there are two tables: one table is to store all contract details & second table is to maintain history forthis.
one condition(col1,col2,col3,col4) are unique combination,we are not creating any PK or FK at database level.evrythng is captured at form level.
if all 4 columns combination exist thn e should not insert that record.
if 4 columns combination doesnot exist then insert into table.
I have used just pre insert,pre update triggers.
I think its a basic form functionality ,by itself it inserts ,update record.now it is doing the same thng.
But I have to add the above condition ,how can i do that.
Pl provide me some ex code .
Thank you.
Hope any one can help me

Answer 1

SQL> create table t
  2  (object_id    number
  3  ,object_name  varchar2(30));
Table created.
SQL>
SQL> create sequence t_seq;
Sequence created.
SQL>
SQL> insert into t (object_id, object_name)
  2  select t_seq.nextval
  3        ,object_name
  4  from   all_objects
  5  ;
52637 rows created.