If you attempt to create a materialized view that includes an aggregate in a subquery, what happens?

• A. Not allowed
• B. Allowed
• C. Only allowed if deterministic
• D. Only with a special privilege

Answer: (A)

Materialized views are designed to be kept up to date automatically through incremental maintenance. When the defining query includes an aggregate inside a subquery, the engine would have to manage complex, nested recomputations in response to every data change, which Snowflake does not support for materialized views. That makes this pattern invalid for a materialized view definition. If you need the same kind of result, restructure so the aggregation happens at the top level of the MV, or create a separate MV or view for the inner query and then perform the aggregation in an outer query.