Oracle's primary key (Primary key) usage detailed ____oracle

Oracle/plsql: Primary key (Primary key) usage 1 Goals

Examples explain how to create, delete, disable, and open primary keys.

2 Preface-What is a primary key

In Oracle, a primary key refers to a single data table column or union of data table columns (Union PRIMARY key | Compound primary key) that uniquely identifies a record. The Data table column data used by the primary key cannot contain null values. Also, a table can contain only one primary key.

Note: In an Oracle database, there are no more than 32 columns for a federated primary key. A primary key can be defined or defined by the ALTER TABLE syntax when creating a table.

3 Creating a primary key-defining a primary key when creating a table

Single column PRIMARY Key example:

CREATE TABLE tb_pk_example
(
  ID number,
  NAME varchar2,
  DESCRIPTION varchar2)
  , CONSTRAINT tb_pk_example_pk PRIMARY Key (ID)--Defines the primary key
);

Federated PRIMARY Key Example:

CREATE TABLE tb_supplier_ex
(
  supplier_id number,
  supplier_name varchar2 (m),
  Supplier_ Description Varchar2 (+), contact_name varchar2 (constraint) TB_SUPPLIER_EX_PK primary
  key (supplier_ ID, Supplier_name)--Joint primary key
);

4 Creating a primary key-using ALTER TABLE syntax

Grammar

ALTER TABLE table_name ADD CONSTRAINT constraint_name PRIMARY KEY (col1, col2,... coln);

Sample preparation

First create two tables (Tb_employees and Tb_departments), and the script is as follows:

CREATE TABLE Tb_employees
(
employee_id number,
employee_name varchar2 (m),
employee_age number,
Employee_birth Date,
department_id number
);

CREATE TABLE Tb_departments
(
department_id number,
department_name varchar2 (MB),
location VARCHAR2 ()
);

Create a primary key with the ALTER TABLE syntax:

--Single row primary key
ALTER TABLE tb_employees add constraint TB_EMPLOYEES_PK primary key (employee_id);
--Joint PRIMARY key
ALTER TABLE tb_departments add constraint TB_DEPARTMENTS_PK primary key (Department_id,department_name);

5 Disabling primary keys

Grammar:

ALTER TABLE table_name DISABLE CONSTRAINT constraint_name;

Example:

ALTER TABLE tb_employees disable constraint tb_employees_pk;

6 Enable primary key

Grammar:

ALTER TABLE table_name ENABLE CONSTRAINT constraint_name;

Example:

ALTER TABLE tb_employees enable constraint tb_employees_pk;

7 Delete primary key

Grammar:

ALTER TABLE table_name DROP CONSTRAINT constraint_name;

Example:

ALTER TABLE tb_employees drop constraint tb_employees_pk;
ALTER TABLE tb_departments drop constraint tb_departments_pk;
ALTER TABLE tb_pk_example drop constraint tb_pk_example_pk;
ALTER TABLE TB_SUPPLIER_EX drop constraint tb_supplier_ex_pk;

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