获取表字段：
select *
from user_tab_columns
where Table_Name= upper('用户表')
order by column_name
获取表注释：
select *
from user_tab_comments
where Table_Name=upper('用户表')
order by Table_Name
获取字段注释：
select *
from user_col_comments
where Table_Name=upper('用户表')
order by column_name
注意：upper方法是必须要的，不要忽视掉了