Answer: JOIN

The question asks which operations can be performed on Snowflake external tables. External tables in Snowflake are read-only and do not support DML operations like INSERT, UPDATE, or DELETE. However, they support query operations including JOIN, which allows them to be used in SELECT statements with other tables. While ALTER is a DDL operation that can modify external table metadata (e.g., adding columns or refreshing metadata), the community discussion highlights that the question focuses on 'operations' in the context of data querying, making JOIN the most appropriate answer. The consensus, supported by upvoted comments and Snowflake documentation, emphasizes that JOIN is a valid operation for external tables, whereas ALTER, while technically possible, is not a data operation in the same sense. Thus, B (JOIN) is the correct choice based on the question's intent and community reasoning.

Author: LeetQuiz Editorial Team