These three statements are true according to the Snowflake documentation and the web search

results. A row access policy is a feature that allows filtering rows based on user-defined conditions. A

row access policy can be applied to an external table, which is a table that reads data from external

files in a stage. However, there are some limitations and considerations for using row access policies

with external tables.

An external table can be created with a row access policy by using the WITH ROW ACCESS POLICY

clause in the CREATE EXTERNAL TABLE statement. The policy can be applied to the VALUE column,

which is the column that contains the raw data from the external files in a VARIANT data type1.

A row access policy can also be applied to the VALUE column of an existing external table by using

the ALTER TABLE statement with the SET ROW ACCESS POLICY clause2.

A row access policy cannot be directly added to a virtual column of an external table. A virtual

column is a column that is derived from the VALUE column using an expression. To apply a row

access policy to a virtual column, the policy must be applied to the VALUE column and the expression

must be repeated in the policy definition3.

External tables are not supported as mapping tables in a row access policy. A mapping table is a table

that is used to determine the access rights of users or roles based on some criteria. Snowflake does

not support using an external table as a mapping table because it may cause performance issues or

errors4.

While cloning a database, Snowflake clones the row access policy, but not the external table.

Therefore, the policy in the cloned database refers to a table that is not present in the cloned

database. To avoid this issue, the external table must be manually cloned or recreated in the cloned

database4.

A row access policy can be applied to a view created on top of an external table. The policy can be

applied to the view itself or to the underlying external table. However, if the policy is applied to the

view, the view must be a secure view, which is a view that hides the underlying data and the view

definition from unauthorized users5.

Reference:

CREATE EXTERNAL TABLE | Snowflake Documentation

ALTER EXTERNAL TABLE | Snowflake Documentation

Understanding Row Access Policies | Snowflake Documentation

Snowflake Data Governance: Row Access Policy Overview

Secure Views | Snowflake Documentation