1.获取表：
select table_name from user_tables; //当前用户拥有的表      
select table_name from all_tables; //所有用户的表 
select table_name from dba_tables; //包括系统表
select table_name from dba_tables where owner=‘用户名‘
 
2.获取表字段：
select * from user_tab_columns where Table_Name=‘用户表‘;
select * from all_tab_columns where Table_Name=‘用户表‘;
select * from dba_tab_columns where Table_Name=‘用户表‘;

3.获取表注释：
select * from user_tab_comments
user_tab_comments：table_name,table_type,comments
相应的还有dba_tab_comments，all_tab_comments，这两个比user_tab_comments多了ower列。

4.获取字段注释：
select * from user_col_comments
user_col_comments：table_name,column_name,comments
相应的还有dba_col_comments，all_col_comments，这两个比user_col_comments多了ower列。

-- 1.你可以先看下这两个表中都有哪些字段信息
select * from user_tab_columns where TABLE_NAME = ‘MEM_LEVEL_TEMP_HISTORY‘;
select * from user_col_comments where TABLE_NAME = ‘MEM_LEVEL_TEMP_HISTORY‘;

-- 2.核心sql: 可以更具你的需求修改
select
t.COLUMN_NAME as "字段名",
decode(c.COMMENTS, null, ‘ ‘, c.COMMENTS) as "含义",
decode(t.DATA_TYPE, ‘TIMESTAMP(6)‘, t.DATA_TYPE, ‘NUMBER‘, (t.DATA_TYPE || ‘(‘ || t.DATA_PRECISION || ‘)‘), (t.DATA_TYPE || ‘(‘ || t.CHAR_LENGTH || ‘)‘)) as "长度",
-- t.DATA_TYPE || ‘(‘ || t.CHAR_LENGTH || ‘)‘ as "类型(长度)",
--  t.CHAR_LENGTH as "字段长度",
t.NULLABLE AS "是否为空",
‘ ‘ as "备注"
from USER_TAB_COLUMNS t join USER_COL_COMMENTS c on c.TABLE_NAME = t.TABLE_NAME and t.COLUMN_NAME = c.COLUMN_NAME
where c.TABLE_NAME = ‘MEM_LEVEL_TEMP_HISTORY‘   --表名应该大写
order by t.COLUMN_ID
;