Which of the following is a valid example of an external table partition column expression?

• A. col1 varchar as (parse_json(metadata$external_table_partition):col1::varchar)
• B. col1 int as (to_number(metadata$external_table_partition):col1)
• C. path varchar as (metadata$path)
• D. filename varchar as (metadata$filename)

Answer: (A)

External table partition columns derive their values from the partition metadata provided by Snowflake, which is exposed as metadata$external_table_partition and stored as JSON. To create a partition column, you extract the needed field from that JSON and cast it to the desired data type. The valid example does exactly that: it parses the JSON, accesses the field named col1, and casts it to varchar. This cleanly yields the partition value for that column.

The other options don’t correctly pull the partition value from the JSON metadata (or misuse the metadata). They either try to use a different metadata field without extracting the partition value, or present invalid syntax for extracting the JSON field, so they won’t produce the proper partition key.