Best way to JOIN with OWB 10.2

Question

Hi Gurus,
im a newbie in working with OWB and i also apologize for my englisch. I have the following Issue. Im using Oracle warehousebuilder and i want to load data in a new Table as Table3 from two distinct source table Table1 and Table2.
It should look like this: Table3.col1 = Table1.col2 ; Table3.col2 = Table1.col3; Table3.col3 = Table2.colb.
I mean it is a kind of JOIN but the column from Table3 have to be just the same as the column from Table1 and Table2 and no other combination.
Table1 : col1 | col2 | col3
Table2: cola | colb | colc
Table3: Table1.col2 | Table1.col3 | Table2.colb
Can someone help me?
Thx

Answer 1

Vinzsanity,
The problem is that you are trying to model a query that requires something more than a simple join as you seem to hope..
Joining based on simple table row order is not something relational databases are really designed to do well. They join on values. For example, if you simply try to write basic SQL to make your join you discover the problem:
select t1.col1, t2.colb
from   table1 a,
         table2  b
where a.rownum = b.rownum ;What you get is an ORA-01747 error as the rownum psuedocolumn is not valid in this context. But if you don't find a way to join on roworder you get the crossproduct - which is NOT what you want.
The simplest pure SQL join to get your results as described in your sample data is:
select a.col1, b.cola
from   (select rownum rnum, s.* from table1 s) a,
         (select rownum rnum, t.* from table2 t) b
where a.rnum(+) = b.rnum;but this only implies a possible one-way outer join to meet your described data sample. If you want a full outer join to handle the possibilities where either table could have more or less rows than the other, then
select a.col1, b.cola
from   ((select rownum rnum, s.* from table1 s) a
         full outer join
       (select rownum rnum, t.* from table2 t) b
       on (a.rnum = b.rnum))Now, clearly this is NOT going to me modelled as just a simple join in OWB. First, you need to find a way to add the rownum pseudocolumn to both table result sets in order to be able to join on them. For example, you could use an expression object for each table, dump all of the fields straight from the expression input to the expression output, and then add a rownum column to the output as well. Then join the two with a joiner defined as full outer join on the two rownum fields and map the required columns to the target table.
Or, you could create a view:
Create or replace view table1_And_2_outer_join as
select a.*, b.*
from   ((select rownum rnum1, s.* from table1 s) a
         full outer join
       (select rownum rnum2, t.* from table2 t) b
       on (a.rnum = b.rnum))And use that view as the source object in your mapping.
Or create two views:
Create or replace view table1_with_rownum as
select rownum rnum1, s.* from table1;
Create or replace view table2_with_rownum as
select rownum rnum2, t.* from table2 tAnd then use the two views as your sources and join them together using the joiner object defined as outer join on the rownumber values.
Any of those three options will get you what you seem to want.
Cheers,
Mike