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 --