Update when values differ

Question

Seems this should be obvious, but my limited experience with OWB has not led me to quick solution. I am migrating data to a newer design. Old table "CHANGES" included some updatable columns where the new values overwrite original values (although available from a different "ORIG" table via foreign key). New design has table "ALL" that includes columns for both original and changed values. Original values will be populated and the column for changed values will be NULL until a change actually occurs.
Example (for a given product_id):
A) ORIG.price=10, CHANGES.price=12 will become
ALL.price=10, ALL.price_ch=12.
B) ORIG.price=10, CHANGES.price=10 will become
ALL.price=10, ALL.price_ch=NULL.
I want to pretty much just map the old CHANGES table to the new ALL table, except for these original/changed values. Referring to previous example, the ALL.price column will be populated with all values from ORIG.price.
ALL.price_ch will only be populated if CHANGES.price != ORIG.price.
I have looked at Match/Merge, Key lookup, Target Filter for Update (with column load attributes), when I thought I had it, it was too complex (or screwed up) and OWB got confused. I know that I could break up the map to first load orig values, then separate map to do each change parameter (different cardinality) and tie together with process flows, but I just assume there must be a simpler way thay you gurus out there do all the time.
Thanks for any feedback,
- Randy

Answer 1

Hi Randy
Thanks for the request and maybe I have an idea for you. Perhaps I am overly simplifying the situation, but here goes.
I think you ought to use an Expression. This is the object that looks like (X+Y). Here is a workflow:
1. Drag an Expression object from the palette onto your workspace
2. Drag mappings from both the ORIG.price and CHANGES.price to the INGRP1 of the Expression
3. Right click on the heading for OUTGRP1 and from the pop up box select Edit. This opens an Expression editor
4. In the Expression editor, click on the tab entitled Output Attributes
5. Click the Add button at the bottom right hand corner of the screen
6. A new output item will be added. Edit this to replace the name OUTPUT1 with a suitable name for your calculated item, then enter the datatype and other pieces of the definition as needed
7. Click OK - this closes the Expresion editor - and you should see that your new item has been added to the OUTGRP1
8. Right click on the heading for the new item, and from the popup box select Attribute Properties
9. In the Attribute Properties dialog box, click in the grey area alongside the new item and then click on the little [...] button. This opens an Expression dialog box
10. In the Expresion dialog box you need to enter the SQL that will define the new item. I would use a DECODE something like this:
DECODE(ORIG_Price, CHANGES_Price, NULL, CHANGES_Price)
This can be read as follows:
IF Original Price = Changed Price
THEN use NULL
ELSE use the Changed Price
11. Click OK to close the Expression editor
12. Close the Attribute Properties dialog box
13. Map this new item to ALL.price_ch and I believe you have a solution.
I hope this helps
Regards
Michael