Oracle 增删列,为列增加注释,修改主键等

DROP TABLE STUDY;

DROP TABLE STUDENT;

DROP TABLE COURSE;

/

CREATE TABLE STUDENT

(

SID VARCHAR(10),

SName varchar(30),

primary key (SID)

);

/

CREATE TABLE COURSE

(

CID VARCHAR(10),

CName varchar(50),

primary key (CID)

);

/

CREATE TABLE STUDY

(

SID VARCHAR(10),

CID VARCHAR(10),

SCORE INTEGER DEFAULT 0 CHECK (SCORE between 0 and 100),

constraint PK_STUDY PRIMARY KEY (SID) --注意此处设置主键约束名,便于后面修改表的主键

);

/

COMMIT;

/

select * from student;

select * from study;

/

--以表 student,study,score 为例

--1.增加列

alter table student add (sex varchar2(2) DEFAULT '女',age integer,address varchar(100)) ;

/

--2.修改列定义

ALTER TABLE student MODIFY sex VARCHAR2(4) DEFAULT '男';

/

--3.删除列

ALTER TABLE student DROP COLUMN address;

/

--4.修改列名

ALTER TABLE student RENAME COLUMN sid to sno;

/

ALTER TABLE student RENAME COLUMN sno to sid;

/

--5.修改表名

RENAME study TO Learn;

/

RENAME Learn TO study;

/

--6.增加注释

-- 给表添加释

COMMENT ON TABLE STUDY IS '学习信息表';

/

--给列添加注释

COMMENT ON COLUMN STUDY.SID IS '学员编号';

/

--7.增加外键关联

ALTER TABLE study ADD CONSTRAINT FK_study_R_student_S FOREIGN KEY (SID) REFERENCES student(SID);

/

--8.修改主键

--查找主键约束名

select T.constraint_name from USER_CONSTRAINTS T where table_name='STUDY' and constraint_type='P' AND ROWNUM<2;

/

--删除主键约束

ALTER TABLE study DROP CONSTRAINT PK_STUDY

/

--添加主键

alter table study add constraint PK_STUDY primary key (cid,sid);

/

commit;

/

select * from student;

select * from study;

select * from COURSE;

/