select * from TEST3 t select object_type, count(object_type) from user_objects group by object_type order by object_type select table_name from dba_tables where lower(table_name) = 'tf_dev' --7-1 确定会话可以访问那些对象。 -- 7-1-1 确定模式中各种类型的对象 列出所有对象 select object_type, count(object_type) from user_objects group by object_type --7-1-2 确定有权访问的总数 select object_type, count(object_type) from all_objects group by object_type --7-1-3 确定谁拥有当前登录人能够看到的对象 select distinct owner from all_objects ----------------------------------------------------- --显示表中的数据类型 describe test3; -- user_tab_cols用来获取对应用户表的列信息; -- user_col_comments用来获取对应用户表列的注释信息; -- user_constraints用来获取用户表的约束条件; -- user_cons_columns约束中用户可访问列。 select column_name, data_type, nullable, data_length, data_precision, data_scale from user_tab_columns where table_name = 'TF_DEV' select trunc(sysdate) from dual --创建表 create table tf_dev_copy as select * from tf_dev --创建表结构 create table tf_dev_copy2 as select * from tf_dev where 1=2 select * from tf_dev_copy where rownum<10 select * from test3 --新怎列 alter table test3 add(id number) --修改列 alter table test3 modify(num default 0) --删除列 alter table test3 drop column id --蒋列标记为未使用 alter table test3 set unused column id alter table test3 drop unused columns --重命名列名 alter table test3 rename column num to tnum --删除表 drop table test3