On Insert Trigger Query

Question

Hi All,
I have a procedure which inserts records in table A .
Without changing the procedure I want to check if new record inserted by procedure is existing in table B. If exists in table B skip the record.
Can somebody please advise me the best practice in the situation .
Thanks

Answer 1

Example :
--Session 1
SQL> create table table1 (id number);
Table created.
SQL>
SQL> create table table2(id number);
Table created.
SQL>
SQL> insert into table2 values (1);
1 row created.
SQL>
SQL>
SQL> create or replace trigger table1_trg
  2  before insert or update on table1
  3  for each row
  4  declare
  5  duplicate EXCEPTION;
  6  ct number;
  7  begin
  8      select id into ct from table2 where id=:new.id;
  9      raise duplicate;
10      exception when no_data_found then null;
11                when duplicate then raise_application_error(num=>-20001, msg=>'Record key is already in table2');
12  end;
13  /
Trigger created.
SQL> 
SQL> select * from table1;
no rows selected
SQL> select * from table2;
        ID
         1
SQL> insert into table1 values (1);
insert into table1 values (1)
ERROR at line 1:
ORA-20001: Record key is already in table2
ORA-06512: at "H89UCBAC.TABLE1_TRG", line 8
ORA-04088: error during execution of trigger 'H89UCBAC.TABLE1_TRG'
--You're happy, you have an error as you want
SQL>
SQL> insert into table1 values (2);
1 row created.
--You're happy, it works because id=2 is not into table2
SQL>
SQL> select * from table1;
        ID
         2
SQL> select * from table2;
        ID
         1
SQL> commit;
Commit complete.
Session 1 Add a value in table2
SQL> insert into table2 values (3);
1 row created.
Session 2 Add a value in table1
SQL> insert into table1 values (3);
1 row created.
Session 1 commit
SQL> commit;
Commit complete.
Session 2 commit
SQL> commit;
Commit complete.
--Unfortunately, I have the id=3 in the two tables
SQL> select * from table1;
        ID
         2
         3
SQL> select * from table2;
        ID
         1
         3
SQL>
SQL>
SQL> To resume, it's better to implement the control on application level.
Nicolas.