Answer: UNION without ALL

The Query Profile showing a UnionAll operator with an extra Aggregate operator on top indicates the use of UNION without ALL in the SQL query. When UNION (without ALL) is used, Snowflake must perform duplicate elimination on the combined result sets, which requires an aggregation step. This is why the Aggregate operator appears above the UnionAll operator. The community discussion consistently identifies option C as correct with 100% consensus and upvoted explanations that align with Snowflake documentation. Options A (exploding joins), B (inefficient pruning), and D (queries too large for memory) describe different query performance issues not related to the UnionAll with Aggregate pattern.

Author: LeetQuiz Editorial Team