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COMMENT(7) Postgres-XL 9.5r1.5 Documentation COMMENT(7)

COMMENT - define or change the comment of an object

COMMENT ON
{
  AGGREGATE  aggregate_name ( aggregate_signature ) |
  CAST ( source_type AS target_type) |
  COLLATION  object_name |
  COLUMN  relation_name.column_name |
  CONSTRAINT  constraint_name ON table_name |
  CONSTRAINT  constraint_name ON DOMAIN domain_name |
  CONVERSION  object_name |
  DATABASE  object_name |
  DOMAIN  object_name |
  EXTENSION  object_name |
  EVENT TRIGGER  object_name |
  FOREIGN DATA WRAPPER  object_name |
  FOREIGN TABLE  object_name |
  FUNCTION  function_name ( [ [ argmode ] [ argname ] argtype [, ...] ] ) |
  INDEX  object_name |
  LARGE OBJECT  large_object_oid |
  MATERIALIZED VIEW  object_name |
  OPERATOR  operator_name (left_type, right_type) |
  OPERATOR CLASS  object_name USING index_method |
  OPERATOR FAMILY  object_name USING index_method |
  POLICY  policy_name ON table_name |
  [ PROCEDURAL ] LANGUAGE  object_name |
  ROLE  object_name |
  RULE  rule_name ON table_name |
  SCHEMA  object_name |
  SEQUENCE  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 |
  TRANSFORM FOR  type_name LANGUAGE lang_name |
  TRIGGER  trigger_name ON table_name |
  TYPE  object_name |
  VIEW  object_name
} IS ' text'
where aggregate_signature is:
* | [ argmode ] [ argname ] argtype [ , ... ] | [ [ argmode ] [ argname ] argtype [ , ... ] ] ORDER BY [ argmode ] [ argname ] argtype [ , ... ]

COMMENT stores a comment about a database object.
Only one comment string is stored for each object, so to modify a comment, issue a new COMMENT command for the same object. To remove a comment, write NULL in place of the text string. Comments are automatically dropped when their object is dropped.
For most kinds of object, only the object's owner can set the comment. Roles don't have owners, so the rule for COMMENT ON ROLE is that you must be superuser to comment on a superuser role, or have the CREATEROLE privilege to comment on non-superuser roles. Of course, a superuser can comment on anything.
Comments can be viewed using psql's \d family of commands. Other user interfaces to retrieve comments can be built atop the same built-in functions that psql uses, namely obj_description, col_description, and shobj_description (see Table 9.62, “Comment Information Functions”).

object_name
 
relation_name.column_name
 
aggregate_name
 
constraint_name
 
function_name
 
operator_name
 
policy_name
 
rule_name
 
trigger_name
The name of the object to be commented. Names of tables, aggregates, collations, conversions, domains, foreign tables, functions, indexes, operators, operator classes, operator families, sequences, text search objects, types, and views can be schema-qualified. When commenting on a column, relation_name must refer to a table, view, composite type, or foreign table.
table_name
 
domain_name
When creating a comment on a constraint, a trigger, a rule or a policy these parameters specify the name of the table or domain on which that object is defined.
source_type
The name of the source data type of the cast.
target_type
The name of the target data type of the cast.
argmode
The mode of a function or aggregate argument: IN, OUT, INOUT, or VARIADIC. If omitted, the default is IN. Note that COMMENT does not actually pay any attention to OUT arguments, since only the input arguments are needed to determine the function's identity. So it is sufficient to list the IN, INOUT, and VARIADIC arguments.
argname
The name of a function or aggregate argument. Note that COMMENT does not actually pay any attention to argument names, since only the argument data types are needed to determine the function's identity.
argtype
The data type of a function or aggregate argument.
large_object_oid
The OID of the large object.
left_type
 
right_type
The data type(s) of the operator's arguments (optionally schema-qualified). Write NONE for the missing argument of a prefix or postfix operator.
PROCEDURAL
This is a noise word.
type_name
The name of the data type of the transform.
lang_name
The name of the language of the transform.
text
The new comment, written as a string literal; or NULL to drop the comment.

There is presently no security mechanism for viewing comments: any user connected to a database can see all the comments for objects in that 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, don't put security-critical information in comments.

Attach a comment to the table mytable:
COMMENT ON TABLE mytable IS 'This is my table.';
Remove it again:
COMMENT ON TABLE mytable IS NULL;
Some more examples:
COMMENT ON AGGREGATE my_aggregate (double precision) IS 'Computes sample variance';
COMMENT ON CAST (text AS int4) IS 'Allow casts from text to int4';
COMMENT ON COLLATION "fr_CA" IS 'Canadian French';
COMMENT ON COLUMN my_table.my_column IS 'Employee ID number';
COMMENT ON CONVERSION my_conv IS 'Conversion to UTF8';
COMMENT ON CONSTRAINT bar_col_cons ON bar IS 'Constrains column col';
COMMENT ON CONSTRAINT dom_col_constr ON DOMAIN dom IS 'Constrains col of domain';
COMMENT ON DATABASE my_database IS 'Development Database';
COMMENT ON DOMAIN my_domain IS 'Email Address Domain';
COMMENT ON EXTENSION hstore IS 'implements the hstore data type';
COMMENT ON FOREIGN DATA WRAPPER mywrapper IS 'my foreign data wrapper';
COMMENT ON FOREIGN TABLE my_foreign_table IS 'Employee Information in other database';
COMMENT ON FUNCTION my_function (timestamp) IS 'Returns Roman Numeral';
COMMENT ON INDEX my_index IS 'Enforces uniqueness on employee ID';
COMMENT ON LANGUAGE plpython IS 'Python support for stored procedures';
COMMENT ON LARGE OBJECT 346344 IS 'Planning document';
COMMENT ON MATERIALIZED VIEW my_matview IS 'Summary of order history';
COMMENT ON OPERATOR ^ (text, text) IS 'Performs intersection of two texts';
COMMENT ON OPERATOR - (NONE, integer) IS 'Unary minus';
COMMENT ON OPERATOR CLASS int4ops USING btree IS '4 byte integer operators for btrees';
COMMENT ON OPERATOR FAMILY integer_ops USING btree IS 'all integer operators for btrees';
COMMENT ON POLICY my_policy ON mytable IS 'Filter rows by users';
COMMENT ON ROLE my_role IS 'Administration group for finance tables';
COMMENT ON RULE my_rule ON my_table IS 'Logs updates of employee records';
COMMENT ON SCHEMA my_schema IS 'Departmental data';
COMMENT ON SEQUENCE my_sequence IS 'Used to generate primary keys';
COMMENT ON SERVER myserver IS 'my foreign server';
COMMENT ON TABLE my_schema.my_table IS 'Employee Information';
COMMENT ON TABLESPACE my_tablespace IS 'Tablespace for indexes';
COMMENT ON TEXT SEARCH CONFIGURATION my_config IS 'Special word filtering';
COMMENT ON TEXT SEARCH DICTIONARY swedish IS 'Snowball stemmer for Swedish language';
COMMENT ON TEXT SEARCH PARSER my_parser IS 'Splits text into words';
COMMENT ON TEXT SEARCH TEMPLATE snowball IS 'Snowball stemmer';
COMMENT ON TRANSFORM FOR hstore LANGUAGE plpythonu IS 'Transform between hstore and Python dict';
COMMENT ON TRIGGER my_trigger ON my_table IS 'Used for RI';
COMMENT ON TYPE complex IS 'Complex number data type';
COMMENT ON VIEW my_view IS 'View of departmental costs';

There is no COMMENT command in the SQL standard.
2017 Postgres-XL 9.5r1.5

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