oracle alter table详解
//建测试表
create table dept(
deptno number(3) primary key,
dname varchar2(10),
loc varchar2(13)
);
create table employee_info(
empno number(3),
deptno number(3),
ename varchar2(10),
sex char(1),
phone number(11),
address varchar2(50),
introduce varchar2(100)
);
--
//0.重命名
//0.1 表:rename dept to dt;
rename dt to dept;
//0.2 列:alter table dept rename column loc to location;
alter table dept rename column location to loc;
//1.添加约束
//1.1 primary key
alter table employee_info add constraint pk_emp_info primary key(empno);
//1.2 foreign key
alter table employee_info add constraint fk_emp_info foreign key(deptno)
references dept(deptno);
//1.3 check
alter table employee_info add constraint ck_emp_info check
(sex in ('F','M'));
//1.4 not null
alter table employee_info modify phone constraint not_null_emp_info not null;
//1.5 unique
alter table employee_info add constraint uq_emp_info unique(phone);
//1.6 default
alter table employee_info modify sex char(2) default 'M';
//2.添加列
alter table employee_info add id varchar2(18);
alter table employee_info add hiredate date default sysdate not null;
//3.删除列
alter table employee_info drop column introduce;
//3.修改列
//3.1 修改列的长度
alter table dept modify loc varchar2(50);
//3.2 修改列的精度
alter table employee_info modify empno number(2);
//3.3 修改列的数据类型
alter table employee_info modify sex char(2);
//3.4 修改默认值
alter table employee_info modify hiredate default sysdate+1;
//4.禁用约束
alter table employee_info disable constraint uq_emp_info;
//5.启用约束
alter table employee_info enable constraint uq_emp_info;
//6.延迟约束
alter table employee_info drop constraint fk_emp_info;
alter table employee_info add constraint fk_emp_info foreign key(deptno)
references dept(deptno)
deferrable initially deferred;
//7.向表中添加注释
comment on table employee_info is 'information of employees';
//8.向列添加注释
comment on column employee_info.ename is 'the name of employees';
comment on column dept.dname is 'the name of department';
//9.清除表中所有数据
truncate table employee_info;
//10.删除表
drop table employee_info;
--
//下面来看看刚刚才我们对表dept和表employee_info所做的更改
//user_constraints视图里面包含了刚刚才我们创建的所有约束，以及其他信息，
//你可以用desc user_constraints命令查看其详细说明
select constraint_name,constraint_type,status,deferrable,deferred
from user_constraints
where table_name='EMPLOYEE_INFO';
--
CONSTRAINT_NAME CONSTRAINT_TYPE STATUS DEFERRABLE DEFERRED
------------------------------ --------------- -------- -------------- ---------
PK_EMP_INFO P ENABLED NOT DEFERRABLE IMMEDIATE
FK_EMP_INFO R ENABLED DEFERRABLE DEFERRED
NOT_NULL_EMP_INFO C ENABLED NOT DEFERRABLE IMMEDIATE
SYS_C005373 C ENABLED NOT DEFERRABLE IMMEDIATE
UQ_EMP_INFO U ENABLED NOT DEFERRABLE IMMEDIATE
CK_EMP_INFO C ENABLED NOT DEFERRABLE IMMEDIATE
//我们可以通过user_cons_columns视图查看有关列的约束信息；
select owner,constraint_name,table_name,column_name
from user_cons_columns
where table_name='EMPLOYEE_INFO';
--
OWNER CONSTRAINT_NAME TABLE_NAME COLUMN_NAME
------------------------------ ------------------------------ ------------------------------ ---------------
YEEXUN PK_EMP_INFO EMPLOYEE_INFO EMPNO
YEEXUN CK_EMP_INFO EMPLOYEE_INFO SEX
YEEXUN NOT_NULL_EMP_INFO EMPLOYEE_INFO PHONE
YEEXUN SYS_C005373 EMPLOYEE_INFO HIREDATE
YEEXUN UQ_EMP_INFO EMPLOYEE_INFO PHONE
YEEXUN FK_EMP_INFO EMPLOYEE_INFO DEPTNO
//我们将user_constraints视图与user_cons_columns视图连接起来
//查看约束都指向哪些列
column column_name format a15;
select ucc.column_name,ucc.constraint_name,uc.constraint_type,uc.status
from user_constraints uc,user_cons_columns ucc
where uc.table_name=ucc.table_name and
uc.constraint_name=ucc.constraint_name and
ucc.table_name='EMPLOYEE_INFO';
--
COLUMN_NAME CONSTRAINT_NAME CONSTRAINT_TYPE STATUS
--------------- ------------------------------ --------------- --------
EMPNO PK_EMP_INFO P ENABLED
DEPTNO FK_EMP_INFO R ENABLED
PHONE NOT_NULL_EMP_INFO C ENABLED
HIREDATE SYS_C005373 C ENABLED
PHONE UQ_EMP_INFO U ENABLED
SEX CK_EMP_INFO C ENABLED
--
//这里有个constraint_type，他具体指下面几种类型:
//C:check,not null
//P:primary key
//R:foreign key
//U:unique
//V:check option
//O:read only
--
//我们可以通过user_tab_comments视图获得对表的注释
select * from user_tab_comments
where table_name='EMPLOYEE_INFO';
TABLE_NAME TABLE_TYPE COMMENTS
------------------------------ ----------- --------------------------
EMPLOYEE_INFO TABLE information of employees
--
//我们还可以通过user_col_comments视图获得对表列的注释：
select * from user_col_comments
where table_name='EMPLOYEE_INFO';
--
TABLE_NAME COLUMN_NAME COMMENTS
------------------------------ ------------------------------ ---------------------------
EMPLOYEE_INFO EMPNO
EMPLOYEE_INFO DEPTNO
EMPLOYEE_INFO ENAME the name of employees
EMPLOYEE_INFO SEX
EMPLOYEE_INFO PHONE
EMPLOYEE_INFO ADDRESS
EMPLOYEE_INFO ID
EMPLOYEE_INFO HIREDATE
--
select * from user_col_comments
where table_name='EMPLOYEE_INFO' and
comments is not null;
--
TABLE_NAME COLUMN_NAME COMMENTS
------------------------------ ------------------------------ ------------------------
EMPLOYEE_INFO ENAME the name of employees
--
//最后我们来查看一下修改后的表:
desc employee_info;
Name Type Nullable Default Comments
-------- ------------ -------- --------- ---------------------
EMPNO NUMBER(2)
DEPTNO NUMBER(3) Y
ENAME VARCHAR2(10) Y the name of employees
SEX CHAR(2) Y 'M'
PHONE NUMBER(11)
ADDRESS VARCHAR2(50) Y
ID VARCHAR2(18) Y
HIREDATE DATE sysdate+1
--
desc dept;
Name Type Nullable Default Comments
------ ------------ -------- ------- ----------------------
DEPTNO NUMBER(3)
DNAME VARCHAR2(10) Y the name of department
LOC VARCHAR2(50) Y
--