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Updated on 2024-10-14 GMT+08:00
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COMMENT

Function

COMMENT defines or changes the comment of an object.

Precautions

  • Each object stores only one comment. Therefore, you need to modify a comment and issue a new COMMENT command to the same object. To delete the comment, write NULL at the position of the text string. When an object is deleted, the comment is automatically deleted.
  • Currently, there is no security protection for viewing comments. Any user connected to a database can view all the comments for objects in the database. For shared objects such as databases, roles, and tablespaces, comments are stored globally so any user connected to any database in the cluster can see all the comments for shared objects. Therefore, do not put security-critical information in comments.
  • To comment objects, you must be an object owner or user granted the COMMENT permission. The system administrator has this permission by default.
  • Roles do not have owners, so the rule for COMMENT ON ROLE is that you must be an administrator to comment on an administrator role, or have the CREATEROLE permission to comment on non-administrator roles. A system administrator can comment on all objects.

Syntax

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COMMENT ON
{
  AGGREGATE agg_name (agg_type [, ...] ) |
  CAST (source_type AS target_type) |
  COLLATION object_name |
  COLUMN { table_name.column_name | view_name.column_name } |
  CONSTRAINT constraint_name ON table_name |
  CONVERSION object_name |
  DATABASE object_name |
  DOMAIN object_name |
  EXTENSION object_name |
  FOREIGN DATA WRAPPER object_name |
  FOREIGN TABLE object_name |
  FUNCTION function_name ( [ {[ argname ] [ argmode ] argtype} [, ...] ] ) |
  INDEX object_name |
  LARGE OBJECT large_object_oid |
  OPERATOR operator_name (left_type, right_type) |
  OPERATOR CLASS object_name USING index_method |
  OPERATOR FAMILY object_name USING index_method |
  [ PROCEDURAL ] LANGUAGE object_name |
  ROLE object_name |
  RULE rule_name ON table_name |
  SCHEMA object_name |
  SERVER object_name |
  TABLE object_name |
  TABLESPACE object_name |
  TEXT SEARCH CONFIGURATION object_name |
  TEXT SEARCH DICTIONARY object_name |
  TEXT SEARCH PARSER object_name |
  TEXT SEARCH TEMPLATE object_name |
  TYPE object_name |
  VIEW object_name
}
   IS 'text';

Parameter Description

  • agg_name

    Specifies the new name of an aggregation function.

  • agg_type

    Specifies the data type of the aggregation function parameters.

  • source_type

    Specifies the source data type of the cast.

  • target_type

    Specifies the target data type of the cast.

  • object_name

    Specifies the name of an object.

  • table_name.column_name

    view_name.column_name

    Specifies the column whose comment is defined or modified. You can add the table name or view name as the prefix.

  • constraint_name

    Specifies the table constraint whose comment is defined or modified.

  • table_name

    Specifies the name of a table.

  • function_name

    Specifies the function whose comment is defined or modified.

  • argmode,argname,argtype

    Specifies the schema, name, and type of the function parameters.

  • large_object_oid

    Specifies the OID of the large object whose comment is defined or modified.

  • operator_name

    Specifies the name of the operator.

  • left_type,right_type

    Specifies the data type of the operator parameters (optionally schema-qualified). If the prefix or suffix operator does not exist, the NONE option can be added.

  • text

    Specifies the comment content.

Examples

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openGauss=# CREATE TABLE tpcds.customer_demographics_t2
(
    CD_DEMO_SK                INTEGER               NOT NULL,
    CD_GENDER                 CHAR(1)                       ,
    CD_MARITAL_STATUS         CHAR(1)                       ,
    CD_EDUCATION_STATUS       CHAR(20)                      ,
    CD_PURCHASE_ESTIMATE      INTEGER                       ,
    CD_CREDIT_RATING          CHAR(10)                      ,
    CD_DEP_COUNT              INTEGER                       ,
    CD_DEP_EMPLOYED_COUNT     INTEGER                       ,
    CD_DEP_COLLEGE_COUNT      INTEGER
)
WITH (ORIENTATION = COLUMN,COMPRESSION=MIDDLE)
DISTRIBUTE BY HASH (CD_DEMO_SK);

-- Comment out the tpcds.customer_demographics_t2.cd_demo_sk column.
openGauss=# COMMENT ON COLUMN tpcds.customer_demographics_t2.cd_demo_sk IS 'Primary key of customer demographics table.';

-- Create a view consisting of rows with c_customer_sk less than 150.
openGauss=# CREATE VIEW tpcds.customer_details_view_v2 AS
    SELECT *
    FROM tpcds.customer
    WHERE c_customer_sk < 150;

-- Comment out the tpcds.customer_details_view_v2 view.
openGauss=# COMMENT ON VIEW tpcds.customer_details_view_v2 IS 'View of customer detail';

-- Delete the view.
openGauss=# DROP VIEW tpcds.customer_details_view_v2;

-- Delete tpcds.customer_demographics_t2.
openGauss=# DROP TABLE tpcds.customer_demographics_t2;
Parent topic: SQL Syntax