Oracle -- table operation

grammar ：

CREATE TABLE schema_name.table_name (
    column_1 data_type column_constraint,
    column_2 data_type column_constraint,
    ...
    table_constraint
 );

Case study 1： Create tables directly , Do not set constraints

CREATE TABLE tbl_students (
	stu_num CHAR(10) NOT NULL,
	stu_name VARCHAR2(10) NOT NULL,
	stu_sex CHAR(4) NOT NULL,
	stu_age NUMBER(3),
	stu_tel NUMBER(11)
)

//  Add a new column to the student table 
ALTER TABLE tbl_students ADD stu_email VARCHAR2(20);

//  newly added 
ALTER TABLE tbl_students ADD stu_email VARCHAR2(20);

//  Modify the column , Only modification of types and constraints is supported 
ALTER TABLE tbl_students MODIFY stu_email VARCHAR2(50)

//  Delete column 
ALTER TABLE tbl_students DROP COLUMN stu_email

//  Delete table 
DROP TABLE PERSONS;

notes ：alter Cannot conflict with itself , For example, gender preservation men ,3 Characters , It will be revised again 2 One character will report an error

> ORA-01441: cannot decrease column length because some value is too big

Case study 2： Primary key

Primary key One or more fields in a data table , Used to uniquely represent a piece of data in a data table
The field of the primary key is unique and not empty , It is divided into single column primary keys and multi column primary keys

Single column primary key ：

Once created , When viewing the design table , You can see the key

//  Create a primary key when creating a table 
CREATE TABLE tbl_students (
	stu_num CHAR(10) primary key,
	stu_name VARCHAR2(10) NOT NULL,
	stu_sex CHAR(2) NOT NULL,
	stu_age NUMBER(3),
	stu_tel NUMBER(11)
)

CREATE TABLE tbl_students (
	stu_num CHAR(10),
	stu_name VARCHAR2(10) NOT NULL,
	stu_sex CHAR(2) NOT NULL,
	stu_age NUMBER(3),
	stu_tel NUMBER(11),
	primary key(stu_num)
)

//  Add constraints to columns  
ALTER TABLE tbl_students ADD CONSTRAINTS pk_student primary key(stu_num)

  notes ： The modification of adding a primary key cannot conflict with itself , Watch stu_num Not marked as not null when , If the data doesn't null, You can also add constraints , But if the data has null Or repeat , May be an error , Cause adding failure

> ORA-01449: column contains NULL values; cannot alter to NOT NULL

ORA-02437: cannot validate (WATERBOSSFACTORY.PK_STUDENT) - primary key violated（ Use duplicate values ）

Case study 3： Combined the primary key

Use two or more fields as primary keys

//  Create a federated primary key 
CREATE TABLE tbl_grads(
	course_id char(3),
	course_name VARCHAR2(50) ,
	stu_num CHAR(10),
	stu_name VARCHAR2(10),
	score NUMBER(3),
	primary key (course_id,stu_num)
)

//  The following will report an error , ORA-02260: table can have only one primary key
CREATE TABLE tbl_grads(
	course_id char(3) primary key,
	course_name VARCHAR2(50) ,
	stu_num CHAR(10),
	stu_name VARCHAR2(10),
	score NUMBER(3) primary key
)

ALTER TABLE tbl_grads ADD CONSTRAINTS pk_grads primary key(course_id,stu_num)

The federated primary key only

  notes ：

（1） As long as there is an empty field or the field where the union primary key is located is repeated , Insert data or alter Adding a primary key will fail

ORA-01449: column contains NULL values; cannot alter to NOT NULL

> ORA-02437: cannot validate (WATERBOSSFACTORY.PK_GRADS) - primary key violated  Both fields repeat

Case study 4： Foreign key constraints

  Primary foreign key Association , That is, the value of the restricted foreign key field must come from the associated field in other data tables , It's usually a primary key

//  Specify foreign keys when creating tables   If the table associated with the foreign key does not exist , May be an error  ORA-00942: table or view does not exist
CREATE TABLE tbl_students(
	stu_num CHAR(10) primary key,
	stu_name VARCHAR2(10) NOT NULL,
	stu_sex CHAR(4) NOT NULL,
	stu_age NUMBER(3),
	stu_tel NUMBER(11),
	stu_cid CHAR(3) not NULL,
	CONSTRAINT fk_student_classes foreign key (stu_cid) references tbl_classes(class_id) on DELETE cascade
)

// on delete cascade When deleting the primary key of the class table , The relevant data in the student table will also be deleted 

//  Add a foreign key constraint 
ALTER TABLE tbl_students ADD CONSTRAINTS fk_student_classes foreign key (stu_cid) references tbl_classes(class_id) on DELETE cascade;

//  Delete foreign key constraint 
ALTER TABLE TBL_STUDENTS DROP CONstraints fk_student_classes;

notes ：

（1） The deletion logic of the two tables is that the class table must be deleted first , Then delete the student table , Because the foreign key of the student table points to the primary key of the class table

（2） Set up on delete cascade after , When deleting the data in the class table , Students in the class will be deleted at the same time

Case study 5：CHECK constraint

Check constraints , Used to limit the values that can be entered in each column , To ensure the correctness of the data

//  add to check constraint 
CREATE TABLE tbl_students(
	stu_num CHAR(10) primary key,
	stu_name VARCHAR2(10) NOT NULL,
	stu_sex CHAR(4) NOT NULL,
	stu_age NUMBER(3),
	stu_tel NUMBER(11),
	stu_cid CHAR(3) not NULL,
	CONSTRAINT fk_student_classes foreign key (stu_cid) references tbl_classes(class_id) on DELETE cascade,
	CONSTRAINT ck_student_sex CHECK(stu_sex=' male ' or stu_sex=' Woman '),
	CONSTRAINT ck_student_age CHECK(stu_age BETWEEN 6 AND 30)
)

ALTER TABLE TBL_STUDENTS DROP constraints ck_student_age;

ALTER TABLE tbl_students add constraints ck_student_age CHECK(stu_age BETWEEN 6 AND 30);

Add good check The constraint is followed by ：

  When adding data does not satisfy the constraint , Will report a mistake

 

Case study 6：UNIQUE constraint

Used to limit the uniqueness of a field , There are three ways to add unique keys , One is to add directly in the field unique, One is to use CONSTRANT Appoint , The difference between the two is to add unique The name of the only key is random ,CONSTRANT Is specified .

//  The telephone is the only , Add unique constraints 
CREATE TABLE tbl_students(
	stu_num CHAR(10) primary key,
	stu_name VARCHAR2(10) NOT NULL,
	stu_sex CHAR(4) NOT NULL,
	stu_age NUMBER(3),
	stu_tel NUMBER(11) UNIQUE,
	stu_cid CHAR(3) not NULL ,
	CONSTRAINT fk_student_classes foreign key (stu_cid) references tbl_classes(class_id) on DELETE cascade,
	CONSTRAINT ck_student_sex CHECK(stu_sex=' male ' or stu_sex=' Woman '),
	CONSTRAINT ck_student_age CHECK(stu_age BETWEEN 6 AND 30)
)


CREATE TABLE tbl_students(
	stu_num CHAR(10) primary key,
	stu_name VARCHAR2(10) NOT NULL,
	stu_sex CHAR(4) NOT NULL,
	stu_age NUMBER(3),
	stu_tel NUMBER(11),
	stu_cid CHAR(3) not NULL ,
	CONSTRAINT fk_student_classes foreign key (stu_cid) references tbl_classes(class_id) on DELETE cascade,
	CONSTRAINT uq_student_tel UNIQUE(stu_tel),
	CONSTRAINT ck_student_sex CHECK(stu_sex=' male ' or stu_sex=' Woman '),
	CONSTRAINT ck_student_age CHECK(stu_age BETWEEN 6 AND 30)
)


ALTER TABLE TBL_STUDENTS DROP constraints uq_student_tel;

After adding a unique key, you can view it in the only key

If you add duplicate data , Will report a mistake

  Case study 7：NOT NULL

  Has been used , I won't repeat