【基础操作】1.表操作

-- 1.基本表操作表drop table user1;create table user1(id    number(5,3)  not null,   -- (N,M)  N:一共几位,M:小数后几位name  varchar2(10) not null,tel   number(11,0) not null);truncate table user1;insert into user1(id,name,tel) values(23.456,'aaa',22);insert into user1(id,name,tel) values((select max(id) from user1)+1,'aaa',22);select * from user1;-- 2.创建表create table user2 as select * from user1;         -- 复制全部字段和数据create table user3 as select id,name from user1;   -- 复制指定字段和数据create table user4 as select id gid ,name gname from user1;  -- 新表字段设置为新的名字create table user5 as select id gid ,name gname from user1 where 1=2; -- 复制结构不复制数据-- 3.alter-- 增加字段ALTER TABLE "USER4" ADD ("tel" NUMBER(11) DEFAULT 13900001111  NOT NULL) ;-- 删除字段ALTER TABLE "USER4" DROP("tel");-- 更改表名ALTER TABLE "USER5" RENAME TO "USER55";-- 更改字段名ALTER TABLE "USER4" RENAME COLUMN "tel" TO "randomkey";-- 变更属性ALTER TABLE "USER4" MODIFY ("randomkey" VARCHAR2(11) DEFAULT 'sha256' );-- 修改默认值ALTER TABLE "USER4" MODIFY ("GNAME" VARCHAR2(20),"randomkey" VARCHAR2(20));