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* ÔÚ¶¨ÒåÔ¼ÊøÊ±¿ÉÒÔͨ¹ýCONSTRAINT¹Ø¼ü×ÖÎªÔ¼ÊøÃüÃû£¬Èç¹ûûÓÐÖ¸¶¨£¬ORACLE½«×Ô¶¯ÎªÔ¼Êø½¨Á¢Ä¬ÈϵÄÃû³Æ 
¶¨Òåprimary keyÔ¼Êø(µ¥¸ö×ֶΣ© 
create table employees (empno number(5) primary key,...) 
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create table employees (empno number(5) constraint emp_pk primary key,...) 
¶¨Òåprimary keyÔ¼Êø(¶à¸ö×Ö¶Î,ÔÚ±í¼¶¶¨ÒåÔ¼Êø£© 
create table employees 
(empno number(5), 
deptno number(3) not null, 
constraint emp_pk primary key(empno,deptno) 
using index tablespace indx 
storage (initial 64K 
next 64K 


ORACLE×Ô¶¯»áΪ¾ßÓÐPRIMARY KEYÔ¼ÊøµÄ×Ö¶Î(Ö÷Âë×Ö¶Î)½¨Á¢Ò»¸öΨһË÷ÒýºÍÒ»¸öNOT NULLÔ¼Êø,¶¨ÒåPRIMARY KEYÔ¼ÊøÊ±¿ÉÒÔΪËüµÄË÷Òý 
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alter table employees add primary key (empno) 
alter table employees add constraint emp_pk primary key (empno) 
alter table employees add constraint emp_pk primary key (empno,deptno) 
not nullÔ¼Êø(Ö»ÄÜÔÚ×ֶμ¶¶¨ÒåNOT NULLÔ¼Êø,ÔÚͬһ¸ö±íÖпÉÒÔ¶¨Òå¶à¸öNOT NULLÔ¼Êø) 
alter table employees modify deptno not null/null 
uniqueÔ¼Êø 
create table employees 
( empno number(5), 
ename varchar2(15), 
phone varchar2(15), 
email varchar2(30) unique, 
deptno number(3) not null, 
constraint emp_ename_phone_uk unique (ename,phone) 

alter table employees 
add constraint emp_uk unique(ename,phone) 
using index tablespace indx 
¶¨ÒåÁËUNIQUEÔ¼ÊøµÄ×Ö¶ÎÖв»Äܰüº¬Öظ´Öµ£¬¿ÉÒÔΪһ¸ö»ò¶à¸ö×ֶζ¨ÒåUNIQUEÔ¼Êø,Òò´Ë£¬UNIQUE¼´¿ÉÒÔÔÚ×ֶμ¶Ò²¿ÉÒÔÔÚ±í¼¶¶¨Ò壬 
ÔÚUNIQUEDÔ¼ÊøµÄ×Ö¶ÎÉÏ¿ÉÒÔ°üº¬¿ÕÖµ. 
foreign keyÔ¼Êø 
* ¶¨ÒåΪFOREIGN KEYÔ¼ÊøµÄ×Ö¶ÎÖÐÖ»Äܰüº¬ÏàÓ¦µÄÆäËü±íÖеÄÒýÓÃÂë×ֶεÄÖµ»òÕßNULLÖµ 
* ¿ÉÒÔΪһ¸ö»òÕß¶à¸ö×ֶεÄ×éºÏ¶¨ÒåFOREIGN KEYÔ¼Êø 
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