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Oracle???????

?Oracle??????????????????????????????????????????????????Oracle????????????????

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create table student(    studentid int primary key not null,    studentname varchar(8),    age int);

alter table student rename column oldcolumn to newcolumn;

alter table student add column newcolumn varchar(10);

drop table student;

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insert into student values(2, 'bbb', 13);

delete from student;

truncate table student;

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alter table student drop constraint yy;

alter table student add constraint pk_students primary key (studentid);

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?Oracle???????????????????????????????

alter table emp add constraint fk_emp_dept foreign key (dept) references dept(deptno) on delete cascade;

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alter table emp add constraint fk_emp_dept foreign key (dept) references dept(deptno) on delete set null;

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?Oracle??????to_date????????????

insert into student values('ss12', to_date('21-08-2010 12:21:11', 'DD-MM-YYYY HH:MI:SS'));

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????????????????????ORA-01407:????NULL??????????????????????????NULL????????on delete cascade?on delete set null????

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create table dept(    deptno number(10) not null,    deptname varchar2(30) not null,    constraint pk_dept primary key (deptno));create table emp(    empno number(10) not null,    fname varchar2(20),    lname varchar2(20),    dept number(10),    constraint pk_emp primary key (empno));alter table emp add constraint fk_emp_dept foreign key (dept) references dept(deptno) on delete cascade;insert into dept values(1, '???');insert into dept values(2, '???');insert into emp values(2, 'Mary', 'Song', 1);insert into emp values(3, 'Linda', 'Liu', 2);insert into emp values(4, 'Linlin', 'Zhang', 1);

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?????????????????Oracle?????????