当前用户	所有用户	DBA	备注
user_tables	all_tables	dba_tables	表
user_tab_comments	all_tab_comments	dba_tab_comments	表注释
user_tab_columns	all_tab_columns	dba_tab_columns	表字段
user_col_comments	all_col_comments	dba_col_comments	字段注释
user_objects	all_objects	dba_objects	可访问对象

select c.*
from all_tables a 
inner join all_tab_comments d on d.table_name=a.TABLE_NAME
inner join all_tab_columns b on a.TABLE_NAME=b.TABLE_NAME
inner join all_col_comments c on b.COLUMN_NAME=c.column_name and b.TABLE_NAME=c.TABLE_NAME