- //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
