COMMENT

Description

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 CREATE ROLE 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 |
 
  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 |
  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 |
  TRIGGER trigger_name ON table_name
}
   IS 'text';

Parameters

• 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

-- Create a table.
gaussdb=# CREATE TABLE emp(
    empno varchar(7),
    ename varchar(50),
    job varchar(50),
    mgr varchar(7),
    deptno int
);

-- Add comments to a table.
gaussdb=# COMMENT ON TABLE emp IS 'Department table';

-- Add comments to columns.
gaussdb=# COMMENT ON COLUMN emp.empno  IS  'Employee ID';
gaussdb=# COMMENT ON COLUMN emp.ename  IS  'Employee name';
gaussdb=# COMMENT ON COLUMN emp.job    IS  'Job';
gaussdb=# COMMENT ON COLUMN emp.mgr    IS  'Manager ID';
gaussdb=# COMMENT ON COLUMN emp.deptno IS  'Department ID';

-- View table comments.
gaussdb=# \d+
 Schema |    Name     |   Type   | Owner |    Size    |             Storage              | Description 
--------+-------------+----------+-------+------------+----------------------------------+-------------
 public | emp         | table    | omm   | 0 bytes    | {orientation=row,compression=no} | Department table

-- View column comments.
gaussdb=# \d+ emp
                                 Table "public.emp"
 Column |         Type          | Modifiers | Storage  | Stats target | Description 
--------+-----------------------+-----------+----------+--------------+-------------
 empno  | character varying(7)  |           | extended |              | Employee ID
 ename  | character varying(50) |           | extended |              | Employee name
 job    | character varying(50) |           | extended |              | Job
 mgr    | character varying(7)  |           | extended |              | Manager ID
 deptno | integer               |           | plain    |              | Department ID
Has OIDs: no
Distribute By: HASH(empno)
Location Nodes: ALL DATANODES
Options: orientation=row, compression=no

-- Delete the emp table.
gaussdb=# DROP TABLE emp;