COMMENT — 定义或者更改一个对象的注释
COMMENT ON { ACCESS METHODobject_name
| AGGREGATEaggregate_name
(aggregate_signature
) | CAST (source_type
AStarget_type
) | COLLATIONobject_name
| COLUMNrelation_name
.column_name
| CONSTRAINTconstraint_name
ONtable_name
| CONSTRAINTconstraint_name
ON DOMAINdomain_name
| CONVERSIONobject_name
| DATABASEobject_name
| DOMAINobject_name
| EXTENSIONobject_name
| EVENT TRIGGERobject_name
| FOREIGN DATA WRAPPERobject_name
| FOREIGN TABLEobject_name
| FUNCTIONfunction_name
( [ [argmode
] [argname
]argtype
[, ...] ] ) | INDEXobject_name
| LARGE OBJECTlarge_object_oid
| MATERIALIZED VIEWobject_name
| OPERATORoperator_name
(left_type
,right_type
) | OPERATOR CLASSobject_name
USINGindex_method
| OPERATOR FAMILYobject_name
USINGindex_method
| POLICYpolicy_name
ONtable_name
| [ PROCEDURAL ] LANGUAGEobject_name
| ROLEobject_name
| RULErule_name
ONtable_name
| SCHEMAobject_name
| SEQUENCEobject_name
| SERVERobject_name
| TABLEobject_name
| TABLESPACEobject_name
| TEXT SEARCH CONFIGURATIONobject_name
| TEXT SEARCH DICTIONARYobject_name
| TEXT SEARCH PARSERobject_name
| TEXT SEARCH TEMPLATEobject_name
| TRANSFORM FORtype_name
LANGUAGElang_name
| TRIGGERtrigger_name
ONtable_name
| TYPEobject_name
| VIEWobject_name
} IS 'text
' ACCESS METHODobject_name
| AGGREGATEaggregate_name
(aggregate_signature
) | CAST (source_type
AStarget_type
) | COLLATIONobject_name
| COLUMNrelation_name
.column_name
| CONSTRAINTconstraint_name
ONtable_name
| CONSTRAINTconstraint_name
ON DOMAINdomain_name
| CONVERSIONobject_name
| DATABASEobject_name
| DOMAINobject_name
| EXTENSIONobject_name
| EVENT TRIGGERobject_name
| FOREIGN DATA WRAPPERobject_name
| FOREIGN TABLEobject_name
| FUNCTIONfunction_name
[ ( [ [argmode
] [argname
]argtype
[, ...] ] ) ] | INDEXobject_name
| LARGE OBJECTlarge_object_oid
| MATERIALIZED VIEWobject_name
| OPERATORoperator_name
(left_type
,right_type
) | OPERATOR CLASSobject_name
USINGindex_method
| OPERATOR FAMILYobject_name
USINGindex_method
| POLICYpolicy_name
ONtable_name
| [ PROCEDURAL ] LANGUAGEobject_name
| PUBLICATIONobject_name
| ROLEobject_name
| RULErule_name
ONtable_name
| SCHEMAobject_name
| SEQUENCEobject_name
| SERVERobject_name
| STATISTICSobject_name
| SUBSCRIPTIONobject_name
| TABLEobject_name
| TABLESPACEobject_name
| TEXT SEARCH CONFIGURATIONobject_name
| TEXT SEARCH DICTIONARYobject_name
| TEXT SEARCH PARSERobject_name
| TEXT SEARCH TEMPLATEobject_name
| TRANSFORM FORtype_name
LANGUAGElang_name
| TRIGGERtrigger_name
ONtable_name
| TYPEobject_name
| VIEWobject_name
} IS 'text
' 其中aggregate_signature
是: * | [argmode
] [argname
]argtype
[ , ... ] | [ [argmode
] [argname
]argtype
[ , ... ] ] ORDER BY [argmode
] [argname
]argtype
[ , ... ]
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
(见表 9.68)。
object_name
relation_name
.column_name
aggregate_name
constraint_name
function_name
operator_name
policy_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、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
一个函数或者聚集的参数的模式: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
一个函数或者聚集参数的名称。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
一个函数或者聚集参数的数据类型。
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
。
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。
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 rtree IS 'R-Tree 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 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 STATISTICS my_statistics IS 'Improves planner row estimations'; 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';
SQL 标准中没有COMMENT
命令。