Categories:

Table, View, & Sequence DDL

ALTER MASKING POLICY

Replaces the existing masking policy rules with new rules or a new comment and allows the renaming of a masking policy.

Any changes made to the policy rules go into effect when the next SQL query that uses the masking policy runs.

Syntax

ALTER MASKING POLICY [ IF EXISTS ] <name> SET BODY -> <expression_ON_VAL>

ALTER MASKING POLICY [ IF EXISTS ] <name> RENAME TO <new_name>

ALTER MASKING POLICY [ IF EXISTS ] <NAME> SET COMMENT = '<string_literal>'

Parameters

name

Identifier for the masking policy; must be unique in the parent schema of the policy.

The identifier value must start with an alphabetic character and cannot contain spaces or special characters unless the entire identifier string is enclosed in double quotes (e.g. "My object"). Identifiers enclosed in double quotes are also case-sensitive.

For more details, see Identifier Requirements.

expression_ON_VAL

SQL expression that transforms the data.

The expression can include Conditional Expression Functions to represent conditional logic, built-in functions or UDFs to transform the data.

If a UDF or external function is used inside the masking policy body, the policy owner must have OWNERSHIP on the UDF or external function. Users querying a column that has a masking policy applied to it do not need to have USAGE on the UDF or external function.

RENAME TO new_name

Specifies the new identifier for the masking policy; must be unique for your schema.

For more details, see Identifier Requirements.

COMMENT = 'string_literal'

Adds a comment or overwrites the existing comment for the masking policy.

Default: No value

Usage Notes

  • If you want to update an existing masking policy and need to see the current definition of the policy, call the GET_DDL function or run the DESCRIBE MASKING POLICY command.

  • You cannot change the policy signature (i.e. argument name or input/output data type). If you need to change the signature, execute a DROP MASKING POLICY statement on the policy and create a new one.

  • Before executing an ALTER statement, you can execute a DESCRIBE MASKING POLICY statement to determine the argument name to use for updating the policy.

  • For masking policies that include a subquery in the masking policy body, use EXISTS in the WHEN clause. For a representative example, see the custom entitlement table example in the Examples section in CREATE MASKING POLICY.

  • Moving a masking policy to a managed access schema (using the ALTER MASKING POLICY … RENAME TO syntax) is prohibited unless the masking policy owner (i.e. the role that has the OWNERSHIP privilege on the masking policy) also owns the target schema.

  • Adding a masking policy to a column fails if the column is referenced by a row access policy. For more information, see ALTER ROW ACCESS POLICY.

  • If using a UDF in a masking policy, ensure the data type of the column, UDF, and masking policy match. For more information, see User-defined Functions in a Masking Policy.

  • Regarding metadata:

    Attention

    Customers should ensure that no personal data (other than for a User object), sensitive data, export-controlled data, or other regulated data is entered as metadata when using the Snowflake service. For more information, see Metadata Fields in Snowflake.

Examples

The following example updates the masking policy to use a SHA-512 hash. Users without the ANALYST role see the value as a SHA-512 hash, while users with the ANALYST role see the plain-text value.

DESCRIBE MASKING POLICY email_mask;

-- evaluate output

+-----+------------+---------------+-------------------+-----------------------------------------------------------------------+
| Row | name       | signature     | return_type       | body                                                                  |
+-----+------------+---------------+-------------------+-----------------------------------------------------------------------+
| 1   | EMAIL_MASK | (VAL VARCHAR) | VARCHAR(16777216) | case when current_role() in ('ANALYST') then val else '*********' end |
+-----+------------+---------------+-------------------+-----------------------------------------------------------------------+

ALTER MASKING POLICY email_mask SET BODY ->
  CASE
    WHEN current_role() IN ('ANALYST') THEN VAL
    ELSE sha2(val, 512)
  END;