Generate a surregate key only when insert a new row - (SCD1)

Question

Hi all,
I´m starting with OWB (10gR2) and I'm creating a simple template dimension with SDC type 1 with one source, one target and a sequence do generate the surrogate key.
The main properties configurations are:
- Target property: Loading type = INSERT/UPDATE.
- Only match the natural key between source and target.
- Only use the sequence.nextval when inserting a new row.
- Mapping: Set based.
The generated code was something like this:
{color:#000080}+MERGE INTO DIM_DEFAULT+{color}
{color:#000080}+USING SCR_TABLE+{color}
{color:#000080}+ON(SCR_TABLE.NATURALKEY=DIM_DEFAULT.NATURALKEY)+{color}
{color:#000080}+WHEN MATCHED THEN+{color}
{color:#000080}+UPDATE SET NAME=SCR_TABLE.NAME+{color}
{color:#000080}+WHEN NOT MATCHED THEN+{color}
{color:#000080}+INSERT(SK_DEFAULT,NATURALKEY,NAME)+ {color}
{color:#000080}+VALUES(SQ_DIM_DEFAULT.NEXTVAL,SCR_TABLE.NATURALKEY,SCR_TABLE.NAME)+{color}
Ok, it works fine! But the merge statement generates a new SK for each merged row even if the action is update! What I want is a new SK only when the process inserts a new row. Hard-coding, I possible solve this problem creating a function to return the nextval from a sequence and put it on the insert clause like this:
{color:#000080}+MERGE INTO DIM_DEFAULT+{color}
{color:#000080}+USING SCR_TABLE+{color}
{color:#000080}+ON(SCR_TABLE.NATURALKEY=DIM_DEFAULT.NATURALKEY)+{color}
{color:#000080}+WHEN MATCHED THEN+{color}
{color:#000080}+UPDATE SET NAME=SCR_TABLE.NAME+{color}
{color:#000080}+WHEN NOT MATCHED THEN+{color}
{color:#000080}+INSERT(SK_DEFAULT,NATURALKEY,NAME)+ {color}
{color:#000080}+VALUES(FN_SQC_NEXTVAL('SQ_DIM_DEFAULT'),SCR_TABLE.NATURALKEY,SCR_TABLE.NAME)+{color}
Hard-coded it works fine as I need and that´s the point that I want to know:
It´s possible perform this solution using OWB?
I tried to use Constants but this solution doesn´t work then I tried an expression calling my sequence.nextval function but the result was:
{color:#000080}+MERGE INTO DIM_DEFAULT+{color}
{color:#000080}+USING (SELECT FN_SQC_NEXTVAL('SQ_DIM_DEFAULT') AS SK_DEFAULT_0,NATURALKEY,NAME FROM SCR_TABLE) AS SCR_TABLE+{color}
{color:#000080}+ON(SCR_TABLE.NATURALKEY=DIM_DEFAULT.NATURALKEY)+{color}
{color:#000080}+WHEN MATCHED THEN+{color}
{color:#000080}+UPDATE SET NAME=SCR_TABLE.NAME+{color}
{color:#000080}+WHEN NOT MATCHED THEN+{color}
{color:#000080}+INSERT(SK_DEFAULT,NATURALKEY,NAME)+ {color}
{color:#000080}+VALUES(SK_DEFAULT_0,SCR_TABLE.NATURALKEY,SCR_TABLE.NAME)+{color}
It´s the same of merge the row using the SEQUENCE.NEXTVAL direct.
Does anyone have a workaround to solve this situation?

Answer 1

Hi,
Perhaps this comes a bit late but...
Have you tried to change attribute properties in the mapping? For simple example you have a source table in sa-stage which have to fields: code (varchar2(2), natural key) and description (varchar2(50)). You want to map those fields to target table where you have 3 fields: id (NUMBER(10), surrogate id, nextval from sequence when new row inserted), code (as from the source, natural key, the field to determine if the coming row is new or one to be merged) and description as in source table. Fields and datatypes are just for an example.
When you have source and target tables in your mapping (and fields mapped), drag the sequence operator to the mapping and map the nextval to target table's surrogate id field.
- Change target table operator properties:
* loading type = UPDATE/INSERT
* Match by constraint = no constraint
- Change target table attribute properties for:
* surrogate id field: Load column when updating row = no; match column when updating row = no; load column when inserting row = yes
* natural key field(s): Load column when updating row = no; match column when updating row = yes; load column when inserting row = yes
* all the regular fields: Load column when updating row = yes; match column when updating row = no; load column when inserting row = yes
- change the deleting rules as you want them to be
- Validate your mapping. If the green light is shown, the settings in field properties are suitable for merge.
Hope this is what you wanted to get. I think this kind of solution works fine. Trigger in the table that holds and where one inserts millions of rows sounds scary...
Regards,
jk
Added text: sorry about false alarm. I think that was what you did. The solution above steals the nextvals from sequence. Perhaps no-native-english-reader should be more careful when reading questions ;-)
Edited by: jkoski on 5.11.2008 1:30