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。
每个对象仅存储一个注释字符串，因此，若要修改注释，请针对同一对象发出新的 COMMENT 命令。若要移除注释，请在文本字符串所在位置写入 NULL。在对象删除时，注释将自动删除。
将针对要注释的对象获取 SHARE UPDATE EXCLUSIVE 锁。
对于大多数种类的对象，只有对象的所有者才能设置注释。角色没有所有者，因此 COMMENT ON ROLE 的规则是您必须为超级用户才能对超级用户角色发表评论，或具有 CREATEROLE 特权并且已被授予目标角色的 ADMIN OPTION 特权。同样，访问方法也没有所有者；您必须为超级用户才能对访问方法发表评论。当然，超级用户可以对任何内容发表评论。
可以使用 psql 的 \d 系列命令查看注释。可基于 psql 使用的同一内建函数构建其他用于检索注释的用户界面，即 obj_description、col_description 和 shobj_description（请参见 表 9.80）。
object_namerelation_name.column_nameaggregate_nameconstraint_namefunction_nameoperator_namepolicy_nameprocedure_nameroutine_namerule_nametrigger_name要注释的对象的名称。驻留在模式（表、函数等）中的对象的名称可以是经模式限定的。在评论列时，relation_name 必须引用表、视图、组合类型或外部表。
table_namedomain_name在对约束、触发器、规则或策略创建注释时，这些参数指定定义该对象的表或域的名称。
source_type强制转换的源数据类型的名称。
target_type强制转换的目标数据类型的名称。
argmode所涉及函数、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 并不会真正接收 OUT 参数，因为仅需输入参数即可确定函数标识。因此，仅列出 IN、INOUT 和 VARIADIC 参数。
argname所涉及函数、过程或聚合参数的名称。请注意，COMMENT 并不会真正接收参数名称，因为仅需参数数据类型即可确定函数标识。
argtype所涉及函数、过程或聚合参数的数据类型。
large_object_oid大对象的 OID。
left_typeright_type操作员参数的数据类型（可选择进行模式限定）。对于前缀操作符的缺失参数，编写 NONE。
PROCEDURAL这是一个噪音词。
type_name转换数据类型的名称。
lang_name转换语言的名称。
string_literal用字符串文本形式编写的注释的新内容。
NULL编写 NULL 可删除注释。
目前没有安全机制可用于查看注释：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。对于数据库、角色和表空间等共享对象，注释存储在全局中，因此连接到群集中的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，不要将安全相关信息放在注释中。
附加到表 mytable 的注释
COMMENT ON TABLE mytable IS 'This is my table.';
再次删除它
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。