1.添加注释

--语法
comment on [type] [target] is [comment]  
--为表添加注释
comment on table user is 'The user table';
--为字段注释
comment on column user.userid is 'The user ID';

2.查询注释

--查询字段注释，objsubid为表中字段的序号，从左侧从1开始
select description from pg_description
join pg_class on pg_description.objoid = pg_class.oid
where relname = 'tablename'

--查询表名、表注释
select relname as tabname,
cast(obj_description(relfilenode,'pg_class') as varchar) as comment from pg_class c 
where  relkind = 'r' and relname not like 'pg_%' and relname not like 'sql_%' order by relname

查询字段注释
select description from pg_description join pg_class on pg_description.objoid = pg_class.oid where relname = '表名'