Difference between singleordefault() and firstordefault() , single() and first() - entity framework

// Entity framework

// Difference between singleordefault() and firstordefault()  ,  single() and first() 

 /*

             * Single and SingleOrDefault

            

             * * Single

               It returns a single record if the match found.

               An exception is thrown, if none or more than one match found.

       

             * * SingleOrDefault

               It returns a single record if match found.

               An exception is thrown, if more than one match found. A default value is returned, if no match is found.

            */

            /*First

                It returns first record from the collection if one or more than one match found.

                An exception is thrown, if no match is found.

             * FirstOrDefault

                It returns first record from the collection if one or more than one match found.

                A default value is returned, if no match is found for that element in the collection.

             */

using System;

using System.Collections.Generic;

using System.Linq;

using System.Web;

using System.Web.Mvc;

namespace MyMVC.Controllers

{

    public class PersonController : Controller

    {

        //

        // GET: /Person/

        AdventureConnection connection = new AdventureConnection();

        public ActionResult Index()

        {

            var firstName = connection.People.Where(m => m.BusinessEntityID == 99945).Select(m => m.FirstName).SingleOrDefault();

            //SELECT TOP (2) [Extent1].[FirstName] AS [FirstName] FROM [Person].[Person] AS [Extent1] WHERE 15 = [Extent1].[BusinessEntityID]

            //if there are multiple rows in the table then SingleOrDefault and Single throws error. below line thows error

            //var FirstName = connection.People.Where(m => m.PersonType == "EM").Select(m => m.FirstName).SingleOrDefault();

            //var FirstName = connection.People.Where(m => m.PersonType == "EM").Select(m => m.FirstName).Single();

            //it will select first matching reconrd from database. this will work if there are more matches. if no record found then it will thorw "Sequence contains no elements" exception

            var LastName = connection.People.Where(m => m.PersonType == "LEM").Select(m => m.FirstName).First();

            //SELECT TOP (1) [Extent1].[FirstName] AS [FirstName] FROM [Person].[Person] AS [Extent1] WHERE N'EM' = [Extent1].[PersonType]

            //it will select first matching reconrd from database. this will work if there are more matches.also work if no record found, return null if no record found.

            var MiddleName = connection.People.Where(m => m.PersonType == "LEM").Select(m => m.MiddleName).FirstOrDefault();

            //SELECT TOP (1)  [Extent1].[MiddleName] AS [MiddleName] FROM [Person].[Person] AS [Extent1] WHERE N'EM' = [Extent1].[PersonType]

            ViewBag.firstName = firstName;

            return View();

        }

    }

}