oracle 查看表注释，列注释，列类型

在我们接触一个新的系统时，往往要接触系统的数据库，要了解系统表，最好可以全局的浏览整个系统

select t.TABLE_NAME as 表名,
       a.comments as 表注释,
       t.COLUMN_NAME as 列名,
       s.DATA_TYPE || '(' || s.DATA_LENGTH || ')' as 列类型,
       t.COMMENTS as 列注释
  from user_col_comments t, user_tab_comments a, user_tab_columns s
 where t.comments is not null
   and t.TABLE_NAME = a.TABLE_NAME
   and t.COLUMN_NAME = s.COLUMN_NAME
   and s.table_name = a.TABLE_NAME
 order by t.TABLE_NAME, t.COLUMN_NAME;

select s.TABLE_NAME as 表名, s.comments as 表注释
  from user_tab_comments s
 where s.comments is not null
   and s.table_type = 'TABLE'
 order by s.TABLE_NAME