Prerequisite: Create Table

    create table departments (id NUMBER, name VARCHAR2(100));
    insert into departments(id,name) values (101,'HR');

   create table employees(id NUMBER,name VARCHAR2(20),email VARCHAR2(30) ,gender CHAR(1),department_id NUMBER, salary NUMBER);

   insert into employees (id,name,email,department_id,salary) values
   (1,'Naresh','n@gmail.com',101,10000);

   select * from employees;

Constraints

• NOT NULL
• UNIQUE
• PRIMARY KEY ( UNIQUE + NOT NULL )
• CHECK
• FOREIGN KEY

Task 1: Employee Table Rules

• id - is mandatory and must be unique ( Primary Key)
• name - is mandatory ( Not Null )
• email - is not null and unique ( Not Null + Unique )
• gender - optional and valid values are "M" for Male and "F" for Female
• department_id - must be a valid department
• salary - is optional, must be greater than zero.

    create table employees (
        id NUMBER primary key,
        name VARCHAR2(30) not null,
        email VARCHAR2(40) not null,
        gender CHAR(1),
        department_id NUMBER not null,
        salary NUMBER,
        unique (email),
        check ( gender in ('M','F')),
        foreign key (department_id) references departments(id),
        check (salary > 0 )
    );