COMMENT

为现有对象添加注释或覆盖现有注释。

可以将注释添加到所有对象（用户、角色、仓库、数据库、表等）。您还可使用此命令为各个表列添加注释，但不能为列上的约束添加注释。

语法

COMMENT [ IF EXISTS ] ON <object_type> <object_name> IS '<string_literal>';

COMMENT [ IF EXISTS ] ON COLUMN <table_name>.<column_name> IS '<string_literal>';

参数

ON object_type object_name

将注释添加到具有指定标识符的指定类型（例如，TABLE、SCHEMA、VIEW 等）的对象。

如果标识符包含空格或特殊字符，则整个字符串必须放在双引号内。放在双引号内的标识符也区分大小写。

有关更多信息，请参阅 标识符要求。

ON COLUMN table_name.column_name

向指定的表列添加注释。

如果标识符包含空格或特殊字符，则整个字符串必须放在双引号内。放在双引号内的标识符也区分大小写。

有关更多信息，请参阅 标识符要求。

IS string_literal

指定要添加的注释。

默认：NULL

使用说明

  • 除此命令之外，您还可以在创建或更改对象时添加或修改注释：

  • 在表列上添加或修改注释时使用的语法略有不同：

    • 要在创建时添加注释，请在列声明后加上 COMMENT 关键字（而不是属性）。

    • 要修改注释，请使用此命令。

  • 若要向约束添加注释，请使用 CREATE TABLE 或 CREATE | ALTER TABLE ... CONSTRAINT 命令。

  • DESCRIBE TABLE 输出不显示表约束的注释，例如多列主键。要查看这些注释，请查询 TABLE_CONSTRAINTS 视图。

  • 关于元数据：

    注意

    客户应确保在使用 Snowflake 服务时，不会将个人数据（用户对象除外）、敏感数据、出口管制数据或其他受监管数据作为元数据输入。有关更多信息，请参阅 Snowflake 中的元数据字段。

示例

创建一个带有注释的架构，然后覆盖该注释：

CREATE SCHEMA my_schema COMMENT='this is comment1';

SHOW SCHEMAS LIKE 'my_schema';

+-------------------------------+-----------+------------+------------+---------------+---------+------------------+---------+----------------+------+
| created_on                    | name      | is_default | is_current | database_name | owner   | comment          | options | retention_time | ...  |
|-------------------------------+-----------+------------+------------+---------------+---------+------------------+---------+----------------+------|
| 2025-02-26 12:08:52.363 -0800 | MY_SCHEMA | N          | Y          | MY_DB         | MY_ROLE | this is comment1 |         | 1              |  ... |
+-------------------------------+-----------+------------+------------+---------------+---------+------------------+---------+----------------+------+

COMMENT ON SCHEMA my_schema IS 'now comment2';

SHOW SCHEMAS LIKE 'my_schema';

+-------------------------------+-----------+------------+------------+---------------+---------+--------------+---------+----------------+-----+
| created_on                    | name      | is_default | is_current | database_name | owner   | comment      | options | retention_time | ... |
|-------------------------------+-----------+------------+------------+---------------+---------+--------------+---------+----------------+-----+
| 2025-02-26 12:08:52.363 -0800 | MY_SCHEMA | N          | Y          | MY_DB         | MY_ROLE | now comment2 |         | 1              | ... |
+-------------------------------+-----------+------------+------------+---------------+---------+--------------+---------+----------------+-----+

创建一个带有表列注释的表，然后覆盖该注释：

CREATE OR REPLACE TABLE test_comment_table_column(my_column STRING COMMENT 'this is comment3');

DESC TABLE test_comment_table_column;

+-----------+-------------------+--------+-------+---------+-------------+------------+-------+------------+------------------+-------------+----------------+
| name      | type              | kind   | null? | default | primary key | unique key | check | expression | comment          | policy name | privacy domain |
|-----------+-------------------+--------+-------+---------+-------------+------------+-------+------------+------------------+-------------+----------------|
| MY_COLUMN | VARCHAR(16777216) | COLUMN | Y     | NULL    | N           | N          | NULL  | NULL       | this is comment3 | NULL        | NULL           |
+-----------+-------------------+--------+-------+---------+-------------+------------+-------+------------+------------------+-------------+----------------+

COMMENT ON COLUMN test_comment_table_column.my_column IS 'now comment4';

DESC TABLE test_comment_table_column;

+-----------+-------------------+--------+-------+---------+-------------+------------+-------+------------+--------------+-------------+----------------+
| name      | type              | kind   | null? | default | primary key | unique key | check | expression | comment      | policy name | privacy domain |
|-----------+-------------------+--------+-------+---------+-------------+------------+-------+------------+--------------+-------------+----------------|
| MY_COLUMN | VARCHAR(16777216) | COLUMN | Y     | NULL    | N           | N          | NULL  | NULL       | now comment4 | NULL        | NULL           |
+-----------+-------------------+--------+-------+---------+-------------+------------+-------+------------+--------------+-------------+----------------+

创建带有注释的视图，然后覆盖该注释：

CREATE OR REPLACE VIEW test_comment_view COMMENT='this is comment5' AS (SELECT * FROM test_comment_table_column);

SHOW VIEWS LIKE 'test_comment_view';

+-------------------------------+-------------------+----------+---------------+-------------+---------+------------------+-----+
| created_on                    | name              | reserved | database_name | schema_name | owner   | comment          | ... |
|-------------------------------+-------------------+----------+---------------+-------------+---------+------------------+-----+
| 2025-02-26 12:38:35.440 -0800 | TEST_COMMENT_VIEW |          | MY_DB         | MY_SCHEMA   | MY_ROLE | this is comment5 | ... |
+-------------------------------+-------------------+----------+---------------+-------------+---------+------------------+-----+

COMMENT ON VIEW test_comment_view IS 'now comment6';

SHOW VIEWS LIKE 'test_comment_view';

+-------------------------------+-------------------+----------+---------------+-------------+---------+--------------+-----+
| created_on                    | name              | reserved | database_name | schema_name | owner   | comment      | ... |
|-------------------------------+-------------------+----------+---------------+-------------+---------+--------------+-----+
| 2025-02-26 12:38:35.440 -0800 | TEST_COMMENT_VIEW |          | MY_DB         | MY_SCHEMA   | MY_ROLE | now comment6 | ... |
+-------------------------------+-------------------+----------+---------------+-------------+---------+--------------+-----+