Trigger with :new references

Question

i have a table with the following fields
I_ID I_ID_PARENT      I_Description               ekey
1 1      Pageimpressions
2 1      Startpage
3 1      news
4 1      R_part
5 4      Business
6 4      Finance
7 4      Computer
8 4      carriere &
9 4      Kids
10 4      Shopping
11 4      Travel
i want a trigger which inserts a value into ekey automatically while inserting a new row into a table. the possible records for the table would be as stated abv. the value of ekey shud be some thing like parent||'0'||no.of child of that parent (ex.101,102,103,104,401...)
can u help me out in this process... i have written a code which im sending u below but gives me error
create or replace trigger DLEI_trig
before insert on D_POSITION
for each row when (new.I_ID > 0)
Begin
select to_char(base_key) into :new.EKEY from (
select e1.:new.I_ID*100+ROW_NUMBER()
OVER(
PARTITION BY e1.:new.I_Description order by e1.:new.I_Description desc) base_key
from D_POSITION e1,D_POSITION e2
where e2.:new.I_ID_parent=e1.I_ID) ;
end;
/

Answer 1

This is a solution but it is not transaction safe. It will work if you only ever have one user updating the table; so it might be viable for systems based on Personal Oracle :P
Ponder the following sequence of events, in which two users update a table which has the trigger RAMUTR.
Cheers, APC
User 1 starts the following transaction:
USR1> insert into t1 values (1, 325, 0, 'Does this work?');
1 row created.
USR1> select col1, col3, col4 from t1;
      COL1       COL3 COL4
         1        101 Does this work?
USR1> commit;
Commit complete.
USR1> insert into t1 values (1, 326, 0, 'How about this?');
1 row created.
USR1> select col1, col3, col4 from t1;
      COL1       COL3 COL4
         1        101 Does this work?
         1        102 How about this?
Unfortunately user 1 doesn't commit at this point. So when user 2 starts work this is what happens:
USR2> select col1, col3, col4 from t1;
      COL1       COL3 COL4
         1        101 Does this work?
USR2> insert into t1 values (1, 426, 0, 'Is this right?');
1 row created.
USR2> commit;
Commit complete.
USR2>
Which means user 1 is now in for a bit of a surprise:
USR1> insert into t1 values (1, 326, 0, 'What happened?');
1 row created.
USR1> select col1, col3, col4 from t1;
      COL1       COL3 COL4
         1        101 Does this work?
         1        102 How about this?
         1        102 Is this right?
         1        104 What happened?
USR1>