Which stream type can be used for tracking the records in external tables?

A stream on an external table tracks changes to the set of files in the external stage location. According to the official Snowflake documentation, only append-only streams can be created on external tables. This type of stream is specifically designed to track new files added to the external stage, which are then reflected as new rows in the external table. The stream records these additions, enabling incremental data processing pipelines for data stored in external cloud storage.

B. External: "External" is not a valid stream type in Snowflake. While the stream is created on an external table, the type of the stream itself is append-only.
C. Insert-only: This is a legacy stream type that has been superseded by append-only streams. It is not the designated type for external tables.
D. Standard: Standard streams track all DML changes (INSERT, UPDATE, DELETE). External tables are read-only and do not support UPDATE or DELETE operations, making a standard stream inapplicable.

1. Snowflake Documentation: Streams on External Tables.

Section/Content: "To query change data for external tables, you must create a stream on the external table. Currently, only append-only streams can be created on external tables." This section explicitly states the required stream type.

2. Snowflake Documentation: CREATE STREAM.

Section/Content: Under CREATE STREAM ... ON EXTERNAL TABLE, the syntax and usage notes clarify that the APPENDONLY = TRUE parameter is mandatory when creating a stream on an external table. This enforces the append-only behavior.