Introduction to Classification

This topic provides information on how classification works.

For information on how to use custom classifiers, see Custom Data Classification.


Classification is a multi-step process that associates Snowflake-defined system tags to columns by analyzing the fields and metadata for personal data; this data can be tracked by a data engineer using SQL and Snowsight. A data engineer can classify columns in a table to determine whether the column contains certain kinds of data that need to be tracked or protected, such a unique identifier (passport or bank account data), a quasi-identifier (the city in which the individual lives), or a sensitive value (the salary of an individual).

By tracking the data with a system tag and protecting the data by using a masking or row access policy, the data engineer can improve the governance posture associated with the data. The overall result of the classification and data protection steps is to facilitate compliance with data privacy regulations.

You can classify a single table or tables in a schema. Snowflake provides predefined system tags to enable you to classify and tag columns, or you can use custom classifiers to define your own semantic category based on your knowledge of your data. You can also choose an approach the uses Snowflake system tags and custom classifiers depending on the governance posture that you wish to adopt.

Classification provides the following benefits to data privacy and data governance administrators:

Data access:

The results of classifying column data can inform identity and access management administrators to evaluate and maintain their Snowflake role hierarchies to ensure the Snowflake roles have the appropriate access to sensitive or PII data.

Data sharing:

The classification process can help to identify and confirm the storage location of PII data. Subsequently, a data sharing provider can use the classification results to determine whether to share data and how to make the PII data available to a data sharing consumer.

Policy application:

The usage of columns containing PII data, such as referencing columns in base tables to create a view or materialized view, can help to determine the best approach to protect the data with either a masking policy or a row access policy.

System tags and categories

System tags are tags that Snowflake creates, maintains, and makes available in the shared SNOWFLAKE database. There are two Classification system tags, both of which exist in the SNOWFLAKE.CORE schema:



The data engineer assigns these tags to a column containing personal or sensitive data.

String values:

Snowflake stores the assignment of a system tag on a column as a key-value pair, where the value is a string. Snowflake defines the allowed string values for each classification system tag because Snowflake maintains each of these system tags.

The tag names, SEMANTIC_CATEGORY and PRIVACY_CATEGORY, correspond to the Classification categories that Snowflake assigns to the column data during the column sampling process (i.e. the tag names and category names use the same words):

Semantic category:

The semantic category identifies personal attributes.

A non-exhaustive list of personal attributes Classification supports include name, age, and gender. These three attributes are possible string values when assigning the SEMANTIC_CATEGORY tag to a column.

Classification can detect information from different countries, such as Australia, Canada, and the United Kingdom. For example, if your table column contains phone number information, the analysis process can differentiate the different phone number values from each of these countries.

Privacy category:

If the analysis determines that the column data corresponds to a semantic category, Snowflake further classifies the column to a privacy category. The privacy category has three values: identifier, quasi-identifier, or sensitive. These three values are the string values that can be specified when assigning the PRIVACY_CATEGORY Classification system tag to a column.

  • Identifier: These attributes uniquely identify an individual. Example attributes include name, social security number, and phone number.

    Identifier attributes are synonymous with direct identifiers.

  • Quasi-identifier: These attributes can uniquely identify an individual when two or more or these attributes are in combination. Example attributes include age and gender.

    Quasi-identifiers are synonymous with indirect identifiers.

  • Sensitive: These attributes are not considered enough to identify an individual but are information that the individual would rather not disclose for privacy reasons.

    Currently, the only attribute that Snowflake evaluates as sensitive is salary.

  • Insensitive: These attributes do not contain personal or sensitive information.

The following table summarizes the relationship between each classification category and system tag, and the string values for each classification system tag. Snowflake supports international SEMANTIC_CATEGORY tag values that pertain to certain countries. The country codes are based on the ISO-3166-1 alpha-2 standard. Other semantic categories, such as EMAIL and GENDER, do not have a country code. To track international information, the data engineer uses the value in the SEMANTIC_CATEGORY tag values column when setting a system tag on a column.



Supported countries












  • IBAN

  • IMEI


  • NAME


  • URL

  • VIN

  • CA, NZ, US

  • AU, CA, US

  • AU, NZ

  • CA, GB, NZ, SG, US

  • AU, NZ, SG

  • AU, CA, NZ, SG, US

  • AU, CA, GB, JP, US

  • CA, US

  • AU, NZ




  • CITY


  • AGE











  • CA, NZ, US

  • US

  • CA, NZ, US

  • AU, CA, CH, GB, JP, NZ, US




Multiple semantic tag string values from all three privacy categories can be considered “Sensitive Personal Data”, “Special Categories of Data”, or similar terms under laws and regulations, and might require additional protections or controls.

Currently, Classification does not tag column data as both sensitive and identifying. In other words, when setting the system tag on a given column, you must choose either the SEMANTIC_CATEGORY or PRIVACY_CATEGORY tag.

Supported objects and data types

Snowflake supports classifying data stored in all types of tables and views, including external tables, materialized views, and secure views.

You can classify table and view columns for all supported data types except for the following data types:




    Note that you can classify a column with the VARIANT data type when the column data type can be cast to a NUMBER or STRING data type. Snowflake does not classify the column if the column contains JSON, XML, or other semi-structured data.

If a table contains columns that are not of a supported data type or the column contains all NULL values, the classification process ignores the columns and does not include them in the output.


If your data represents NULL values with a value other than NULL, the accuracy of the classification results may be impacted.

Compute costs

The classification process requires compute resources, which are provided by the virtual warehouse that is in use and running when classification is performed.

The amount of time needed to classify the data in a table/view (and, therefore, the number of credits consumed by the warehouse) is a function of the amount of data to be classified.

In particular, if a table or view has a large number of columns that support classification, the processing time can be impacted. However, as a general rule, the processing speed scales linearly with the warehouse size. In other words, each size increase for a warehouse (X-small to Small) typically reduces the processing time by half.

Use the following general guidelines to select a warehouse size:

  • No concern for processing time: x-small warehouse.

  • Up to 100 columns in a table: small warehouse.

  • 101 to 300 columns in a table: medium warehouse.

  • 301 columns or more in a table: large warehouse.

For details, see Warehouse considerations.


To capitalize on the Classification feature and optimize your PII data tracking capabilities, do the following:


Query Account Usage views first:

  • ACCESS_HISTORY: determine the table and view objects that are accessed most frequently.

  • OBJECT_DEPENDENCIES: determine metadata references between two or more objects.

Use the query results to prioritize schema-level or database-level assignment of the Classification system tags.

Column names:

Use sensible column names in your table objects and train table creators to adhere to internal table creation guidelines.

Data types:

Use sensible data types for columns. For example, an AGE column should have the NUMBER data type.


If a column has a VARIANT data type, use the FLATTEN command on the column prior to classifying the table.


Use the proper warehouse size when classifying data. For details, refer to Compute costs (in this topic).

Manage Classification

Privilege reference

The privilege model for Data Classification enables the data privacy administrator to determine which personas can classify tables and tag columns. For example, a single role can have all of the necessary privileges, or the data privacy administrator can delegate grants to different roles to satisfy separation of duties (SoD) requirements. One example of a viable grant combination is shown in the Get started classifying data section of Use Data Classification.

As an administrator, you have different options depending on how you want to manage which roles or personas are involved. The options provide flexibility the governance posture that you wish to adopt. For example:

  • The table owner (the role with the OWNERSHIP privilege on the table) can classify the table and set system tags on the columns.

  • A custom role that has the SELECT privilege on the table and the APPLY TAG privilege on the account can classify the table and set system tags on the columns.

  • If you want different roles or personas to be involved with classifying and tagging columns, you could grant the SELECT privilege on the table to one role and the APPLY TAG privilege on the account to a different role.

This following table summarizes the different grant options to classify a table, set the Data Classification system tags on columns, and do both of these tasks:

Privilege or role

Classify table(s)

Set system tags on columns

SELECT on the table or view.

OWNERSHIP on the table.

APPLY TAG on the account.


OWNERSHIP on the database or schema.


  • Classifying tables requires a running warehouse. The role that is used to classify a table must have the USAGE privilege on a warehouse at a minimum.

  • You can grant the SNOWFLAKE.GOVERNANCE_VIEWER database role to an account role to enable users with that account role to query the DATA_CLASSIFICATION_LATEST view to see the most recent results of a classified table.

Tracking system tags

Snowflake provides built-in views and functions to track Classification system tag usage:

  • To find the columns with a system tag in your account, query the Account Usage TAG_REFERENCES view:

  • To find the columns with a system tag for a table or view in a specific database, call the TAG_REFERENCES Information Schema table function:

  • To find every tag set on every column in a table or view within a specific database, call the Information Schema TAG_REFERENCES_ALL_COLUMNS table function:

    SELECT * from
  • To find a specific tag value for a column, call the SYSTEM$GET_TAG system function: