PostgreSQL COMMENT

描述

COMMENT存儲關(guān)于一個數(shù)據(jù)庫對象的注釋。

對每一個對象只保存一個注釋字符串，因此為了修改一段注釋，對同一個對象 發(fā)出一個新的COMMENT命令。要移除一段注釋，可在文 本字符串的位置上寫上NULL。當(dāng)對象被刪除時，其注釋 也會被自動刪除。

對大部分類型的對象，只有對象的擁有者可以設(shè)置注釋。角色沒有擁有者，因此 COMMENT ON ROLE的規(guī)則是你必須作為一個超級用戶來對一個 超級用戶角色設(shè)置注釋，或者具有CREATEROLE特權(quán)來對非超級用 戶角色設(shè)置注釋。同樣的，訪問方法也沒有擁有者，你必須作為一個超級用戶來 對一個訪問方法設(shè)置注釋。當(dāng)然，一個超級用戶可以對任何東西設(shè)置注釋。

使用psql的\d 命令家族可以查看注釋。其他檢索注釋的用戶接口可以構(gòu)建在 psql使用的內(nèi)建函數(shù)之上，即 obj_description、col_description 以及shobj_description （見 表 9.73）。

參數(shù)

注解

當(dāng)前對查看注釋沒有安全機制：任何連接到一個數(shù)據(jù)庫的用戶能夠看到 該數(shù)據(jù)庫中所有對象的注釋。對于數(shù)據(jù)庫、角色、表空間這類共享對象， 注釋被全局存儲，因此連接到集簇中任何數(shù)據(jù)庫的任何用戶可以看到共 享對象的所有注釋。因此，不要在注釋中放置有安全性風(fēng)險的信息。

示例

為表mytable附加一段注釋：

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';

兼容性

SQL 標(biāo)準(zhǔn)中沒有COMMENT命令。