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COMMENT ON { TABLE object_name | COLUMN table_name.column_name | AGGREGATE agg_name (agg_type [, ...] ) | CAST (source_type AS target_type) | CONSTRAINT constraint_name ON table_name | CONVERSION object_name | DATABASE object_name | DOMAIN object_name | FUNCTION function_name ( [ [ argmode ] [ argname ] argtype [, ...] ] ) | INDEX object_name | LARGE OBJECT large_object_oid | OPERATOR operator_name (left_type, right_type) | OPERATOR CLASS object_name USING index_method | OPERATOR FAMILY object_name USING index_method | [ PROCEDURAL ] LANGUAGE object_name | ROLE object_name | RULE rule_name ON table_name | SCHEMA object_name | SEQUENCE 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 | TRIGGER trigger_name ON table_name | TYPE object_name | VIEW object_name } IS 'text'
COMMENT存儲一個數(shù)據(jù)庫對象的評注。
要修改一個評注,為同一個對象發(fā)出一條新的COMMENT命令即可。 每個對象只存儲一條評注。要刪除評注,在文本字符串的位置寫上NULL即可。 當刪除對象時,評注自動被刪除掉。
評注可以用命令psql的
\d檢索。其它希望檢索評注的用戶接口可以建筑在psql使用的同樣的內置函數(shù)
obj_description
,col_description
,
和shobj_description
上(參見Table 9-51)。
要加入評注的對象名稱。表、聚集、域、函數(shù)、索引、操作符、操作符類、操作符家庭、序列、全文搜索對象 、類型、視圖,名字可以有模式修飾。
聚集函數(shù)操作的參數(shù)類型,要引用一個零參數(shù)聚集函數(shù),可以使用*代替輸入數(shù)據(jù)類型列表。
類型轉換的源數(shù)據(jù)類型
類型轉換的目標數(shù)據(jù)類型
函數(shù)參數(shù)的模式:IN,OUT, INOUT或者VARIADIC。 請注意COMMENT ON FUNCTION實際上不會注意OUT參數(shù), 因為只要有輸入參數(shù)就可以判斷函數(shù)的身份了。因此, 只要列出IN,INOUT, 和VARIADIC參數(shù)就足夠了。
函數(shù)參數(shù)的名字。請注意COMMENT ON FUNCTION實際上并不關心參數(shù)名, 因為只要有參數(shù)的數(shù)據(jù)類型就可以判斷函數(shù)的身份。
如果有的話,是函數(shù)參數(shù)的數(shù)據(jù)類型(可以用模式修飾)
大對象的OID
這個字沒有任何用處
新的評注,以字符串文本的方式寫;如果是NULL則刪除評注。
目前評注沒有安全機制:任何連接到某數(shù)據(jù)庫上的用戶都可以看到所有該數(shù)據(jù)庫對象的評注(盡管只有超級用戶可以修改不屬于他的對象的評注)。 共享對象(比如數(shù)據(jù)庫、角色、表空間)的評注是全局存儲的,鏈接到任何數(shù)據(jù)庫的任何用戶都可以看到它們。 因此,不要在評注里存放安全敏感地信息。
給表mytable加評注:
COMMENT ON TABLE mytable IS 'This is my table.';
再刪除它:
COMMENT ON TABLE mytable IS NULL;
其它一些例子:
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 COLUMN my_table.my_column IS 'Employee ID number'; COMMENT ON CONVERSION my_conv IS 'Conversion to UTF8'; COMMENT ON DATABASE my_database IS 'Development Database'; COMMENT ON DOMAIN my_domain IS 'Email Address Domain'; 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 OPERATOR ^ (text, text) IS 'Performs intersection of two texts'; COMMENT ON OPERATOR - (NONE, text) IS 'This is a prefix operator on text'; 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 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 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 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標準里沒有COMMENT命令。