COMMENT — 定义或更改对象的注释
COMMENT ON
{
ACCESS METHOD object_name |
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 |
PROCEDURE procedure_name [ ( [ [ argmode ] [ argname ] argtype [, ...] ] ) ] |
PUBLICATION object_name |
ROLE object_name |
ROUTINE routine_name [ ( [ [ argmode ] [ argname ] argtype [, ...] ] ) ] |
RULE rule_name ON table_name |
SCHEMA object_name |
SEQUENCE object_name |
SERVER object_name |
STATISTICS object_name |
SUBSCRIPTION 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 { string_literal | NULL }
where aggregate_signature is:
* |
[ argmode ] [ argname ] argtype [ , ... ] |
[ [ argmode ] [ argname ] argtype [ , ... ] ] ORDER BY [ argmode ] [ argname ] argtype [ , ... ]
COMMENT 存储有关数据库对象的注释。
每个对象只存储一个注释字符串，因此要修改注释，请为同一对象发出新的 COMMENT 命令。要删除注释，请在文本字符串的位置写 NULL。当其对象被删除时，注释会自动删除。
将获取对要注释的对象 SHARE UPDATE EXCLUSIVE 锁。
对于大多数类型的对象，只有对象的拥有者才能设置注释。角色没有拥有者，因此 COMMENT ON ROLE 的规则是，您必须是超级用户才能注释超级用户角色，或者拥有 CREATEROLE 权限，并被授予目标角色的 ADMIN OPTION。同样，访问方法也没有拥有者；您必须是超级用户才能注释访问方法。当然，超级用户可以注释任何内容。
可以使用 psql 的 \d 系列命令查看注释。用于检索注释的其他用户界面可以构建在 psql 使用的相同内置函数之上，即 obj_description、col_description 和 shobj_description（请参阅 表 9.82）。
object_namerelation_name.column_nameaggregate_nameconstraint_namefunction_nameoperator_namepolicy_nameprocedure_nameroutine_namerule_nametrigger_name要注释的对象的名称。位于模式中的对象（表、函数等）的名称可以被模式限定。注释列时，relation_name 必须引用表、视图、复合类型或外部表。
table_namedomain_name在创建约束、触发器、规则或策略的注释时，这些参数指定了定义该对象的表或域的名称。
source_type类型转换的源数据类型的名称。
target_type类型转换的目标数据类型的名称。
argmode函数、过程或聚合参数的模式： IN、OUT、INOUT 或 VARIADIC。如果省略，则默认为 IN。请注意，COMMENT 实际上并不关注 OUT 参数，因为只有输入参数才能确定函数的标识。因此，列出 IN、INOUT 和 VARIADIC 参数就足够了。
argname函数、过程或聚合参数的名称。请注意，COMMENT 实际上并不关注参数名称，因为只有参数数据类型才能确定函数的标识。
argtype函数、过程或聚合参数的数据类型。
large_object_oid大对象的 OID。
left_typeright_type运算符参数的数据类型（可选模式限定）。对于前缀运算符的缺失参数，请写 NONE。
PROCEDURAL这是一个噪声词。
type_name转换的数据类型的名称。
lang_name转换的语言的名称。
string_literal新的注释内容，以字符串字面量表示。
NULL写 NULL 以删除注释。
目前没有查看注释的安全机制：连接到数据库的任何用户都可以看到该数据库中所有对象的注释。对于共享对象（如数据库、角色和表空间），注释是全局存储的，因此连接到集群中任何数据库的任何用户都可以看到所有共享对象的注释。因此，请勿在注释中放置安全敏感信息。
为表 mytable 添加注释
COMMENT ON TABLE mytable IS 'This is my table.';
再次移除它
COMMENT ON TABLE mytable IS NULL;
更多示例
COMMENT ON ACCESS METHOD gin IS 'GIN index access method'; 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 EVENT TRIGGER abort_ddl IS 'Aborts all DDL commands'; 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 PROCEDURE my_proc (integer, integer) IS 'Runs a report'; COMMENT ON PUBLICATION alltables IS 'Publishes all operations on all tables'; COMMENT ON ROLE my_role IS 'Administration group for finance tables'; COMMENT ON ROUTINE my_routine (integer, integer) IS 'Runs a routine (which is a function or procedure)'; 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 STATISTICS my_statistics IS 'Improves planner row estimations'; COMMENT ON SUBSCRIPTION alltables IS 'Subscription for all operations on all tables'; 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 plpython3u 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';
SQL 标准中没有 COMMENT 命令。