(07)oracle新人筆記------約束

NOT NULL

 

CREATE TABLE emp_nn(

empno NUMBER(4),

ename VARCHAR2(10) NOT NULL,

job VARCHAR2(9),

mgr NUMBER(4),

hiredate DATE,

sal NUMBER(7,2),

comm NUMBER(7,2),

deptno NUMBER(7,2) NOT NULL)

 

 

UNIQUE:唯一性約束

賦值了就不能再插入一樣的了，不加NOT NULL就可以插入空值，空值可以重複

 

列級約束

CREATE TABLE deptment(

deptno NUMBER(2),

dname  VARCHAR2(14) CONSTRAINT dept_dname_uk UNIQUE,

loc VARCHAR2(13));

 

表級約束（效果一樣）

CREATE TABLE deptment2(

deptno NUMBER(2),

dname  VARCHAR2(14),

loc VARCHAR2(13),

CONSTRAINT dept_dname_uk2 UNIQUE(dname));

 

 

 

PRIMARY KEY:主鍵約束

列級約束

CREATE TABLE deptment3(

deptno NUMBER(2) CONSTRAINT dept_deptno_pk PRIMARY KEY,

dname  VARCHAR2(14),

loc VARCHAR2(13),

CONSTRAINT dept_dname_uk3 UNIQUE (dname));

 

表級約束

1234123412341234123412433214阿斯頓發士大夫撒放

 

FOREIGN KEY:外鍵約束

CREATE TABLE emp_fk1(

empno NUMBER(4),

ename VARCHAR2(10) NOT NULL,

job VARCHAR2(9),

deptno NUMBER(7,2) NOT NULL CONSTRAINT emp_deptno_fk REFERENCE dept (deptno),

sal NUMBER(7,2));

 

CREATE TABLE emp_fk2(

empno NUMBER(4),

ename VARCHAR2(10) NOT NULL,

job VARCHAR2(9),

deptno NUMBER(7,2) NOT NULL,

CONSTRAINT emp_deptno_fk REFERENCE dept (deptno),

);

 

 

CHECK:檢查性約束

 

 

 

 

刪除約束

 

追加約束

 

約束的啓用與禁用