Delete duplicate row from sql table

--create table with Name Employee
CREATE TABLE Employee
(
id INT,
name VARCHAR(50),
salary INT
)

--Insert records in Employee table
INSERT INTO Employee VALUES(1,'ram',3000)
INSERT INTO Employee VALUES(2,'sita',3000)
INSERT INTO Employee VALUES(3,'Jit',600)
INSERT INTO Employee VALUES(4,'gita',30600)
INSERT INTO Employee VALUES(5,'Jai',3000)
INSERT INTO Employee VALUES(9,'ramu',30500)


--Delete duplicate records using CTE
--Delete records using CTE PARTITION BY id(id is column name)
--IF you have to add duplicate check on more column you can add column name
--Ex:- PARTITION BY id,name,salary ORDER BY id,name,salary

WITH EmployeeCTE AS
(
   SELECT *, ROW_NUMBER() OVER (PARTITION BY id ORDER BY id) AS RowNumber
   FROM Employee
)
DELETE FROM EmployeeCTE WHERE RowNumber > 1

--Delete duplicate records using GROUP BY AND HAVING statement
DELETE  FROM  Employee WHERE id IN (SELECT id FROM Employee GROUP BY id having count(*) >1)

--Delete duplicate records using Temp Variable
SELECT DISTINCT * INTO #tmp FROM Employee
DELETE FROM Employee
INSERT INTO Employee
SELECT * FROM  #tmp DROP TABLE #tmp    

What is covariance and contravariance in c# ?

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
 
namespace ConsoleApp4
{
 
    //>>Allowing you do things in your code that previously 
    //you where surprised  you could not do.
    //-- Anders Hejlsberg
    //>>covariance and contravariance are introduce in .Net 4.0
    class Animal
    {
        public void Walk()
        {
            Console.WriteLine("Animal can walk");
        }
    }
    class Dog : Animal
    {
        public void Walk()
        {
            Console.WriteLine("Dog can walk");
        }
    }
    class Cat : Animal
    {
        public void Walk()
        {
            Console.WriteLine("Cat can walk");
        }
    }
    class Program
    {
        public static void Main(string[] args)
        {
            Animal obj = new Cat();
            obj = new Cat();
 
            //>>Covariance preserves assignment compatbility 
            //between parent and child
            // relationship during dynamic plymorphism
 
            //>>After .Net 4.0 you can also assign group of 
            //objects from child to parents like below
            IEnumerable<Animal> animals = new List<Dog>();
            animals = new List<Cat>();
 
 
 
            Action<Dog> contravarient = DescribeAnimal;
            contravarient(new Dog());
 
 
            Action<Dog> contravarient2 = new Action<Animal>((Animal animal) => { });
 
            Console.ReadKey();
        }
        static void DescribeAnimal(Animal animal)
        {
            Console.WriteLine(animal.GetType().Name);
 
        }
    }
}

.NET Stack and Heap

https://www.youtube.com/watch?v=clOUdVDDzIM