@kd1-1 , One observation is, In both cases the deptid will act as a primary key and it won't allow to insert a duplicate deptid record. However, If you define internal="true", then in Schema structure (in client console UI) you can able to see a key icon near to the attribute.

If it is not defined, then you will find a red exclamation mark symbol near to the attribute. This might leads to a confusion for the campaign operator to understand which one is primary key. So, to avoid confusion be consistent in your schema definitions by adding internal="true" in primary key syntax.
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