本文为您介绍Hologres中注释Comment使用相关内容。
语法介绍
在Hologres中,支持给内部表、外部表、列增加注释(Comment),命令语法如下。语法与PostgreSQL一致,详情请参见COMMENT。Comment可以在建表时使用,也可以建完表之后单独执行。
begin;
create table [schema_name.]table_name ([
{
column_name column_type [column_constraints, [...]]
| table_constraints
[, ...]
}
]);
comment on column <tablename.column> is 'value';--给列加注释
comment on table <tablename> is 'value';--给表加注释
commit;
使用示例
- 建表时添加注释
BEGIN; CREATE TABLE public."user" ( "id" text NOT NULL, "name" text NOT NULL ); COMMENT ON TABLE public."user" is '用户属性表'; COMMENT ON COLUMN public."user".id is '身份证号'; COMMENT ON COLUMN public."user".name is '姓名'; COMMIT;
- 单独执行添加注释。
-- 给表增加注释 COMMENT ON TABLE table_name IS 'my comments on table table_name.'; -- 给列增加注释 COMMENT ON COLUMN table_name.col1 IS 'This my first col1'; -- 给外部表增加注释 COMMENT ON FOREIGN TABLE foreign_table IS ' comments on my foreign table';
通过系统表查看注释
可以通过系统表查看为表、列设置的注释,命令示例如下。
SELECT a.attname as Column,
pg_catalog.format_type(a.atttypid, a.atttypmod) as "Type",
a.attnotnull as "Nullable",
pg_catalog.col_description(a.attrelid, a.attnum) as "Description"
FROM pg_catalog.pg_attribute a
WHERE a.attnum > 0 AND NOT a.attisdropped AND a.attrelid = '<schema.tablename>'::regclass::oid
ORDER BY a.attnum;