(07)oracle新人笔记------约束

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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:唯一性约束

赋值了就不能再插入一样的了，不加NOT NULL就可以插入空值，空值可以重复

列级约束

CREATE TABLE deptment(

deptno NUMBER(2),

dname VARCHAR2(14) CONSTRAINT dept_dname_uk UNIQUE,

loc VARCHAR2(13));

表级约束（效果一样）

CREATE TABLE deptment2(

deptno NUMBER(2),

dname VARCHAR2(14),

loc VARCHAR2(13),

CONSTRAINT dept_dname_uk2 UNIQUE(dname));

PRIMARY KEY:主键约束

列级约束

CREATE TABLE deptment3(

deptno NUMBER(2) CONSTRAINT dept_deptno_pk PRIMARY KEY,

dname VARCHAR2(14),

loc VARCHAR2(13),

CONSTRAINT dept_dname_uk3 UNIQUE (dname));

表级约束

1234123412341234123412433214阿斯顿发士大夫撒放

FOREIGN KEY:外键约束

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:检查性约束

删除约束

追加约束

约束的启用与禁用

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