表的创建、修改及约束

CREATE TABLE EMP2 AS SELECT * FROM EMP WHERE 1=2;--只复制表结构
CREATE TABLE TEST1 AS SELECT EMPNO,ENAME,JOB,SAL FROM EMP WHERE DEPTNO=10;--只复制另一个表中的某几个字段
CREATE TABLE EMP2 AS SELECT * FROM EMP; --复制整张表，包括数据
CREATE TABLE EMP2 AS SELECT * FROM EMP WHERE rownum<=10;--只复制前10行数据

INSERT INTO DEPT VALUES(50,‘DBA‘,‘HK‘);--所有字段都插入值
INSERT INTO DEPT(DEPTNO,DNAME) VALUES(60,‘TEST‘);--只插入其中几个字段值
INSERT INTO EMP2 (SELECT * FROM EMP);--使用子查询插入数据时，不要加values或as
INSERT INTO EMP2 (SELECT * FROM EMP WHERE ROWNUM<=10);

update emp2 set empno=2222,ename=‘rusky‘ where empno=1111;--如果不加where条件，则更新表中的所有行。
update emp2 set (empno,ename)=(2222,‘rusky‘) where empno=1111;--ORA-01767: UPDATE ...SET 表达式必须是子查询 
update emp2 set (ename,job,hiredate)=(select ename,job,hiredate from emp where empno=7369) where empno=1111;--使用子查询修改表
DELETE FROM TEST1 WHERE EMPNO=7782;--删除表中的某一行记录
DELETE FROM TEST;--不加WHERE条件，清空表中所有记录
DELETE FROM EMP2 WHERE DEPTNO=(SELECT DEPTNO FROM DEPT WHERE DNAME=‘SALES‘); --使用子查询删除记录

ALTER TABLE DEPT2 ADD (MANAGER NUMBER(4)); --增加列
ALTER TABLE DEPT2 MODIFY(MANAGER NUMBER(4));--修改列属性
ALTER TABLE DEPT2 DROP COLUMN MANAGER;--删除表中的字段
DROP TABLE DEPT2;--直接删除表，包括表数据和表结构。
TRUNCATE TABLE DEPT2;--只清空表中的数据
RENAME DEPT2 TO DEPT3;--修改表名
COMMENT ON TABLE DEPT3 IS ‘THIS IS A TEST TABLE‘; --给表增加注释
COMMENT ON COLUMN DEPT3.MANAGER IS ‘THE MANAGER OF THIS DEPARTMENT‘;--给某个字段增加注释

SELECT * FROM USER_TABLES; --查看用户所有表
SELECT DISTINCT OBJECT_TYPE FROM USER_OBJECTS; --查看用户拥有的数据类型
SELECT * FROM USER_CATALOG; --查看用户拥有的表、视图、同义词、序列
查看表、字段、视图、同义词等的注释：
ALL_COL_COMMENTS
USER_COL_COMMENTS
ALL_TAB_COMMENTS
USER_TAB_COMMENTS

CREATE TABLE Goods(
GoodsId char(8) primary key, --主键
GoodName varchar2(50),
UnitPrice number(10,2) check(UnitPrice>0),--单价必须大于0
Category varchar2(30),
Provider varchar2(100));
--添加注释
COMMENT ON TABLE Goods is ‘ 商品表Goods（商品号GoodsId，商品名GoodName，单价UnitPrice，商品类别Categroy，供应商Provider）‘

CREATE TABLE Customers(
CustomerId char(8) primary key, --主键
Name varchar2(30) not null,--姓名允许为空
Address varchar2(150),
Email varchar2(100) unique, --Email唯一
Gender char(2) default(‘男‘) check(Gender in(‘男‘,‘女‘)), --性别只能是男或女
CardId char(18));
--添加注释
COMMENT ON TABLE Customers is ‘客户表Customers（客户号CustomerId，姓名Name，住址Address，电邮Email，性别Gender，身份证CardId）‘

CREATE TABLE Purchases(
CustomerId char(8) references Customers(Customerid), --外键
GoodId char(8) references Goods(GoodsId),
Num number(10) check(Num between 1 and 30));
--添加注释
COMMENT ON TABLE Purchases is ‘销售表Purchases（客户号CustomerId，商品号GoodsId，购买数量Num）‘

sql> create table Goods(
GoodsId char(8),GoodsName varchar2(50), Category varchar(30),
constraint PK_GoodsId primary key(GoodsId));

sql>create table Goods(
GoodsId char(8) constraint PK_GoodsId primary key ,--主键
GoodName varchar2(50),
UnitPrice number(10,2) check(UnitPrice>0),--单价必须大于0
Category varchar(30),
Provider varchar(100));

ALTER TABLE Goods modify GoodsId not null;
ALTER TABLE Customers add constraint UQ_CardId unique(Cardid);

sql>alter table 表名 drop constraint 约束名称;
ALTER TABLE Customers drop constraints UQ_CardId;

ALTER TABLE EMPLOYEE RENAME CONSTRAINT PK_EMPLOYEE TO PK_EMPLOYEE1;

列级定义约束：
CREATE TABLE DEPARTMENT(
DEPTID NUMBER(2) PRIMARY KEY,--或者DEPTID NUMBER(2) CONSTRAINT PK_DEPARTMENT PRIMARY KEY,
NAME VARCHAR2(12),
LOC VARCHAR2(12)
);
表级定义约束：
CREATE TABLE EMPLOYEE(
EMPID NUMBER(4),
NAME VARCHAR2(10),
DEPTID NUMBER(2),
CONSTRAINT PK_EMPLOYEE PRIMARY KEY(EMPID),
CONSTRAINT FK_DEPARTMENT FOREIGN KEY(DEPTID) REFERENCES DEPARTMENT(DEPTID)
);

CREATE TABLE DEPARTMENT2(
DEPTID NUMBER(2),--或者DEPTID NUMBER(2) CONSTRAINT PK_DEPARTMENT PRIMARY KEY,
DNAME VARCHAR2(12),
LOC VARCHAR2(12),
PRIMARY KEY(DEPTID,DNAME)
);

CREATE TABLE EMPLOYEE2(
EMPID NUMBER(4) PRIMARY KEY,
NAME VARCHAR2(10),
DEPTID NUMBER(2),
DNAME VARCHAR2(12),
CONSTRAINT FK_DEPARTMENT1 FOREIGN KEY(DEPTID,DNAME) REFERENCES DEPARTMENT2(DEPTID,DNAME) ON DELETE CASCADE--当删除部门表中的某个部门信息时，级联删除员工表中的 
DEPTNO,DNAME.或者这样：ON DELETE SET NULL，设为null
);