The METADATA$ACTION column in a Snowflake stream indicates the type of DML operation that was performed on the source table. According to Snowflake documentation and the community consensus (with AC having 67$ACTION; instead, an UPDATE appears as a DELETE of the old row and an INSERT of the new row. 'TRUNCATE' is not a value in METADATA$ACTION but clears the stream. 'UPSERT' is not a standard DML operation in Snowflake streams and thus not a valid value for METADATA$ACTION.