COMMENT
COMMENT — 定义或者更改一个对象的注释
大纲
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 'text'
其中 aggregate_signature 是：
* |
[ argmode ] [ argname ] argtype [ , ... ] |
[ [ argmode ] [ argname ] argtype [ , ... ] ] ORDER BY [ argmode ] [ argname
] argtype [ , ... ]
描述
COMMENT存储关于一个数据库对象的注释。
对每一个对象只保存一个注释字符串，因此为了修改一段注释，对同一个对象发出一个新的COMMENT命令。要移除一段注释，可在文本字符串的位置上写上NULL。当对象被删除时，其注释也会被自动删除。
对大部分类型的对象，只有对象的拥有者可以设置注释。角色没有拥有者，因此COMMENT ON ROLE的规则是你必须作为一个超级用户来对一个 超级用户角色设置注释，或者具有CREATEROLE特权来对非超级用户角色设置注释。同样的，访问方法也没有拥有者，你必须作为一个超级用户来对一个访问方法设置注释。当然，一个超级用户可以对任何东西设置注释。
使用psql的d 命令家族可以查看注释。其他检索注释的用户接口可以构建在psql使用的内建函数之上，即 obj_description、col_description 以及shobj_description。
参数
object_name
relation_name.column_name
aggregate_name
constraint_name
function_name
operator_name
policy_name
procedure_name
routine_name
rule_name
trigger_name
要被注释的对象的名称。表、聚集、排序方式、转换、域、外部表、函数、 索引、操作符、操作符类、操作符族、存储过程、例程、序列、统计信息、文本搜索对象、类型和 视图的名称可以被模式限定。在注释一列时， relation_name必须 引用一个表、视图、组合类型或者外部表。
table_name
domain_name
当在一个约束、触发器、规则或者策略上创建一段注释时，这些参数指定在其上定义 该对象的表或域的名称。
source_type
造型的源数据类型的名称。
target_type
造型的目标数据类型的名称。
argmode
一个函数，存储过程或者聚集函数的参数的模式：IN、 OUT、INOUT或者VARIADIC。如果被省略，默认值是IN。注意 COMMENT并不真正关心 OUT参数，因为决定函数的身份只需要输入参数。因此列出IN、INOUT和VARIADIC 参数就足够了。
argname
一个函数，存储过程或者聚集函数参数的名称。注意 COMMENT并不真正关心参数名称，因为决定函数的身份只需要参数数据类型。
argtype
一个函数，存储过程或者聚集函数参数的数据类型。
large_object_oid
大对象的 OID。
left_type
right_type
操作符的参数的数据类型（可以是模式限定的）。对一个前缀后后缀操作符 的缺失参数可以写NONE。
PROCEDURAL
这是一个噪声词。
type_name
该转换的数据类型的名称。
lang_name
该转换的语言的名称。
text
写成一个字符串的新注释。如果要删除注释，写成NULL。
注解
当前对查看注释没有安全机制：任何连接到一个数据库的用户能够看到该数据库中所有对象的注释。对于数据库、角色、表空间这类共享对象，注释被全局存储，因此连接到集簇中任何数据库的 任何用户可以看到共享对象的所有注释。因此，不要在注释中放置有安全性风险的信息。
示例
为表mytable附加一段注释：
COMMENT ON TABLE mytable IS 'This is my table.';
移除它：
COMMENT ON TABLE mytable IS NULL;
更多的一些例子：
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 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';