Answer: CREATE, ALTER

According to Snowflake documentation and the community discussion with upvoted comments, clustering keys can be defined during table creation using CREATE TABLE command or after table creation using ALTER TABLE command. The CREATE command allows specifying clustering keys when initially creating the table, while ALTER TABLE enables adding or modifying clustering keys on existing tables. Other options like UPDATE, SET, and SHOW are not valid for defining clustering keys - UPDATE modifies data, SET is used in various contexts but not for clustering keys, and SHOW is for displaying information rather than defining table properties.

Author: LeetQuiz Editorial Team