获取所有的表名和标注释
SELECT
a.TABLE_NAME,b.COMMENTS
FROM
all_tables a left join user_tab_comments b on a.TABLE_NAME=b.TABLE_NAME
WHERE
a.OWNER='数据库名称'
ORDER BY
a.TABLE_NAME
获取所有的表字段，类型，长度和注释
select distinct a.TABLE_NAME,a.COLumn_name,a.data_type,a.data_length,c.comments from all_tab_columns a
inner join all_tables b on a.TABLE_NAME=b.TABLE_NAME and a.OWNER=b.OWNER
inner join all_col_comments c on a.TABLE_NAME=c.TABLE_NAME and a.COLumn_name=c.COLumn_name
where b.OWNER='数据库名称' order by a.TABLE_NAME;