Oracle data integrity

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One 、 Non empty constraint

not null

1、 Create a student table , There are two fields , The first field is id yes number type , The second field is name yes varchar2 Type and cannot be empty .

create table student(
	id number,
	name varchar2 not null,
)

Two 、 Unique constraint

unique

1、 Create a student table , There are two fields , The first field is id yes number type , The second field is name yes varchar2 Type and no repetition is allowed .

Copying tables is actually used to back up tables

create table student(
	id number,
	name varchar2 unique,
)

3、 ... and 、 Primary key constraint

1、 Create a student table , There are two fields , The first field is id yes number Type and primary key , The second field is name yes varchar2 Type and cannot be empty .

create table student(
	id number,
	name varchar2 not null,
	constraint pk_id primary key(id);

Four 、 Composite primary key constraint

1、 Create a student table , There are two fields , The first field is id yes number type , The second field is name yes varchar2 type , And set the two fields as a composite primary key constraint .

create table student(
	id number,
	name varchar2,
	constraint pk_id primary key(id,name);

5、 ... and 、 Check constraint

1、 Create a student table , There are two fields , The first field is id yes number Type and primary key , The second field is name yes varchar2 type , The third is age yes number type , also age stay 0-100 Between .

create table student(
	id number,
	name varchar2,
	age number,
	constraint pk_id primary key(id),
	constraint ck_age check(age between 0 and 100);

6、 ... and 、 Foreign key constraints

1、 Create a student table , There is a field , The first field is id yes number Type and primary key , Create a teacher table , There are two fields , The first field is id yes number type , The second field is sid And for students id The foreign key

create table student(
	id number,
	constraint pk_id primary key(id);

create table teacher(
	id number,
	sid number
	constraint fk_sid foreign key(sid) references student(id);

7、 ... and 、 Modify constraints

1、 Put the student list student Add primary key id Constraints

alter table student add constraint pk_id primary key(id);

2、 Put the student list student Of name Change the field to non empty constraint

alter table student modify(name varchar2 not null);

8、 ... and 、 summary

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The commands involved in the article must be typed several times each like me , Only in the process of knocking can you find out whether you really master the command .

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