Dynamic Lookup in OWB 10.1g

Question

Can we execute dynamic lookup in OWB 10.1g?
I want update the columns of the target table, based on the previous values of the columns.
Suppose there is a record in the target table with previous status and current status columns.
The source table consist of 10 records which need to be processed one at a time in a single batch. Now we need to compare the status of record with the current status of target table. If the source contains next higher status then the current status of target record need to go to previous status and the new status coming from source need to overwrite the current status of target record.
We have tried using row based option as well as setting commit frequency equal to 1 but we are not able to get the required result.
how can we implement this in OWB10.1g?

Answer 1

OK, now what I would do in an odd case like this is to look at the desired FINAL result of a run rather than worry so much about the intermediate steps.
Based on your statement of the status incrementing upward, and only upward, your logic can actually be distilled down to the following:
At the end of the load, the current status for a given primary key is the maximum status, and the previous status will be the second highest status. All the intermediate status values are transitional status values that have no real bearing on the desired final result.
So, let's try a simple prototype:
--drop table mb_tmp_src; /* SOURCE TABLE */
--drop table mb_tmp_tgt; /*TARGET TABLE */
create table mb_tmp_src (pk number, val number);
insert into mb_tmp_src (pk, val) values (1,1);
insert into mb_tmp_src (pk, val) values (1,2);
insert into mb_tmp_src (pk, val) values (1,3);
insert into mb_tmp_src (pk, val) values (2,2);
insert into mb_tmp_src (pk, val) values (2,3);
insert into mb_tmp_src (pk, val) values (3,1);
insert into mb_tmp_src (pk, val) values (4,1);
insert into mb_tmp_src (pk, val) values (4,3);
insert into mb_tmp_src (pk, val) values (4,4);
insert into mb_tmp_src (pk, val) values (4,5);
insert into mb_tmp_src (pk, val) values (4,6);
insert into mb_tmp_src (pk, val) values (5,5);
commit;
create table mb_tmp_tgt (pk number, val number, prv_val number);
insert into mb_tmp_tgt (pk, val, prv_val) values (2,1,null);
insert into mb_tmp_tgt (pk, val, prv_val) values (5,4,2);
commit;
-- for PK=1 we will want a current status of 3, prev =2
-- for PK=2 we will want a current status of 3, prev =2
-- for PK=3 we will want a current status of 1, prev = null
-- for PK=4 we will want a current status of 6, prev = 5
-- for PK=5 we will want a current status of 5, prev = 4
Now, lets's create a pure SQL query that gives us this result:
select pk, val, lastval
from
select pk,
val,
max(val) over (partition by pk) maxval,
lag(val) over (partition by pk order by val ) lastval
from (
select pk, val
from mb_tmp_src mts
union
select pk, val
from mb_tmp_tgt mtt
where val = maxval
(NOTE: UNION, not UNION ALL to avoid multiples where tgt = src, and would want a distinct in the union if multiple instances of same value can occur in source table too)
OK, now I'm not at my work right now, but you can see how unioning (SET operator) the target with the source, passing the union through an expression to get the analytics, and then through a filter to get the final rows before updating the target table will get you what you want. And the bonus is that you don't have to commit per row. If you can get OWB to generate this sort of statement, then it can go set-based.
EDIT: And if you can't figure out how to get OWB to generate thisentirely within the mapping editor, then use it to create a view from the main subquery with the analytics, and then use that as the source in your mapping.
If your problem was time-based where the code values could go up or down, then you would do pretty much the same thing except you want to grab the last change and have that become the current value in your dimension. The only time you would care about the intermediate values is if you were coding for a type 2 SCD, in which case you would need to track all the changes.
Hope this helps.
Mike
Edited by: zeppo on Oct 25, 2008 10:46 AM