I need to run a query which updates a target DE with some rows from another. There is a field called 'origin' which shows on the target data extension where the data came from.
I appreciate this may be more of a generic SQL query but given Marketing Cloud's limited implementation of SQL and some functions being unavailable, I thought I'd ask here...
Basically it will be updating records in the target data extension based on the primary key (subscriber key). Some data exists on various source data extensions. I only want it to fill in the 'origin' field with a value if the field in the target DE is empty/null. If it already has a value in it, I want it left as it is.
I looked at case statements but could only find examples where the decision was made based on a value being in the source DE, rather than the target DE.
For example, I have the current DE:
I'm running queries that pick records up from various DEs and there will be duplication. I'd like to run a query that updated the blank value in the xyz record with 'APP20', but I do not want to overwrite the abc record's 'APP21' value with 'APP20'.