可以参考compat-tools中DBA_COL_COMMENTS视图的实现方式
https://gitee.com/enmotech/compat-tools

SELECT case when n.nspname::text = lower(n.nspname::text) then UPPER(n.nspname::text) else n.nspname::text end AS OWNER
                 , case when c.relname::text = lower(c.relname::text) then UPPER(c.relname::text) else c.relname::text end AS TABLE_NAME
                 , case when a.attname::text = lower(a.attname::text) then UPPER(a.attname::text) else a.attname::text end AS COLUMN_NAME
                 , d.description as COMMENTS
              FROM pg_catalog.pg_attribute a
              JOIN pg_catalog.pg_class c on a.attrelid = c.oid
              JOIN pg_catalog.pg_namespace n on c.relnamespace  = n.oid
              LEFT JOIN pg_catalog.pg_description d on a.attrelid = d.objoid and a.attnum = d.objsubid and d.classoid = 'pg_class'::regclass::oid
             WHERE n.nspname not like 'pg_toast%';

使用类似pg方法

select c.relname,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,pg_tables tb
 where 1=1
   --c.relname = 'sys_user'
  -- and a.attnum > 0
 --  and
-- and  tb.tablename
    and t.typname='bpchar'
   and a.attrelid = c.oid
   and a.atttypid = t.oid
   and d.objoid = a.attrelid
   and d.objsubid = a.attnum;

使用类似mysql方法
information_schema.columns
都满足你的需求。