Data views such as _open and _click have what limitations?

• A. They do not have a primary key, nor can they be indexed
• B. They always have a primary key
• C. They are always indexed by default
• D. They support primary key-based joins

Answer: (A)

Data views like _open and _click are built-in, read-only views that record each tracking event. Because a subscriber can open or click an email multiple times for the same send, there isn’t a single unique row per entity, so no primary key is defined for these views. They also aren’t indexed—the platform doesn’t support adding or relying on indexes on these system views. The practical effect is you can query and analyze these events, but you can’t enforce uniqueness or speed up queries with an index directly on the views; for performance you typically aggregate results or store them in a separate Data Extension. The other statements don’t fit this design, since these views aren’t guaranteed to have a primary key, aren’t indexed by default, and aren’t joined via a primary-key-based mechanism.