1.获取数据库中所有table名：

SELECT   tablename   FROM   pg_tables
WHERE   tablename   NOT   LIKE   'pg%'
AND tablename NOT LIKE 'sql_%'
ORDER   BY   tablename;

2.获取数据库中所有table名及table的注解信息：

SELECT   tablename,obj_description(relfilenode,'pg_class')  FROM   pg_tables  a, pg_class b
WHERE
a.tablename = b.relname
and a.tablename   NOT   LIKE  'pg%'
AND a.tablename NOT LIKE 'sql_%'
ORDER   BY   a.tablename;

3.获取数据库中所有table名及table的注解信息：

SELECT col_description(a.attrelid,a.attnum) as comment,format_type(a.atttypid,a.atttypmod) as type,a.attname as name, a.attnotnull as notnull
FROM pg_class as c,pg_attribute as a
where c.relname = 'tablename' and a.attrelid = c.oid and a.attnum > 0

4.查询字段名、字段类型及字段长度和字段注释：

select a.attnum,a.attname,concat_ws('',t.typname,SUBSTRING(format_type(a.atttypid,a.atttypmod) from '\(.*\)')) as type,d.description from pg_class c, pg_attribute a , pg_type t, pg_description d
where  c.relname = 'table_name' and a.attnum > 0 and a.attrelid = c.oid and a.atttypid = t.oid and  d.objoid=a.attrelid and d.objsubid=a.attnum