Oracle之创建表与修改表详解(四)
NUMBER(4,2)
PRESSTIME DATE
BOOK_NEW NOT NULL VARCHAR2(20)
SCOTT@orcl#alter table mybook5 drop column book_new;
表已更改。
SCOTT@orcl#desc mybook5;
名称 是否为空 类型
--------------------------------------------------------------------------------- --------------------------------------------------
BOOKID NOT NULL NUMBER(10)
BOOKNAME VARCHAR2(40)
AUTHOR VARCHAR2(40)
BOOKPRICE NUMBER(4,2)
PRESSTIME DATE
SCOTT@orcl#alter table mybook5 drop (bookname,author);
表已更改。
SCOTT@orcl#desc mybook5;
名称 是否为空 类型
--------------------------------------------------------------------------------- --------------------------------------------------
BOOKID NOT NULL NUMBER(10)
BOOKPRICE NUMBER(4,2)
PRESSTIME DATE
SCOTT@orcl#alter table mybook5 set unused (bookprice);
表已更改。
SCOTT@orcl#desc mybook5;
名称 是否为空 类型
--------------------------------------------------------------------------------- --------------------------------------------------
BOOKID NOTNULL NUMBER(10)
PRESSTIME DATE
SCOTT@orcl#select * from user_unused_col_tabs;
TABLE_NAME COUNT
----------------------------------------------------------------------
MYBOOK4 1
MYBOOK5 1
SCOTT@orcl#alter table mybook5 drop unused column;
表已更改。
SCOTT@orcl#l
1* alter tablemybook5 drop unused column
SCOTT@orcl#select * from user_unused_col_tabs;
TABLE_NAME COUNT
----------------------------------------------------------------------
MYBOOK4 1
SCOTT@orcl#desc mybook4;
名称 是否为空 类型
--------------------------------------------------------------------------------- --------------------------------------------------
BOOKID NOT NULL NUMBER(10)
PRESS VARCHAR2(40)
PRESSTIME NOT NULL DATE
BOOKNAME NOT NULL VARCHAR2(40)
AUTHOR VARCHAR2(20)
SCOTT@orcl#alter table mybook4 rename column pre