There are addition fuctions that can be done to a table created with SQL vs a PF created with DDS.
IBM statement of direction is there are no plans to add function to DDS in the future.
Here is a link to a web page that has a link on it to hear a pod case SQL vs DDS.
http://www.systemideveloper.com/sessionRoadMap.html

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IMO, the major difference between the two is that data is verified a write-time for a SQL table and at read-time for a DDS PF. There are various other differences (e.g., you cannot add new members to a SQL table), but data integrity has to be at the top of the list. You aren’t allowed to write invalid dates to date fields, you won’t find non-numeric values showing up in numeric fields, etc.

Tom