Linq tutorial for Beginners

What is LINQ?
LINQ stands for Language integrated Query, that allows us to query local object collection or remote data source.

Main Points:
1. Linq data has two parts, sequence and elements. Here names is a sequence and array members are elements.
2. Linq doesn't alter the input sequence. So result will always be in the order it was input.
3. Linq always return an IEnumerable result.
4. "n => n.EndsWith("a")" is a lambda expression that filters the result for us. 

Examples:
// Basic Query
// To achieve  Select * From Product  you need to write follofing linq Query

var Result1 = from p in db.Product                  select p;

// To achieve  Select ProductID, ProductName, Price From Product you need to write follofing linq Query

var Result = from p in db.Product                  select new {                      p.ProductID,                      p.ProductName,                      p.Price                  };

// Where Clause Query
// To achieve  Select * From Product Where ProductID = 1 you need to write follofing linq Query  

var Result = from p in db.Product                  where p.ProductID == 1                  select p;

// To achieve Select * From Product Where SupplierId =3 and Price > 10 you need to write follofing linq Query    

var Result = from p in db.Product                  where p.SupplierID == 3 && p.Price > 10                  select p;

// To achieve Select * From Product Where SupplierId =2 Or SupplierId=5 you need to write follofing linq Query

var Result = from p in db.Product                  where p.SupplierID == 2 || p.SupplierID == 5                  select p;

// Order By Query
//To achieve   Select * From Product Order By ProductId you need to write follofing linq Query

var Result = from p in db.Product                  orderby p.ProductID                  select p;

// To achieve  Select * From Product Order By ProductId Desc you need to write follofing linq Query

var Result = from p in db.Product                  orderby p.ProductID descending                  select p;

// To achieve  Select * From Product Order By CategoryId, Price Desc you need to write follofing linq Query   

var Result = from p in db.Product                  orderby p.CategoryID, p.Price descending                  select p;

// Top Query
//To achieve Select Top 5 * From Product you need to write follofing linq Query

var Result = (from p in db.Product                  select p).Take(5);

//To achieve Select Top 1 * From Product you need to write follofing linq Query

var Result = (from p in db.Product                    select p).Take(1);      or     var Result = (from p in db.Product                    select p).First();

// Distinct Query
//To achieve Select Distinct CategoryId From Product you need to write follofing linq Query

var Result = (from p in db.Product                    select p.CategoryID).Distinct();

// Group By Query
//To achieve Select CategoryId, Count(CategoryID) As FieldName From Product Group By CategoryId you need to write follofing linq Query

var Result = from p in db.Product                   group p by p.CategoryID into g                   select new {                       CategoryId = g.Key,                       FieldName = g.Count()                   };

//To achieve Select CategoryId, Avg(UnitPrice) As NewField From Product Group By CategoryId you need to write follofing linq Query

var Result = from p in db.Product                   group p by p.CategoryID into g                   select new {                       CategoryId = g.Key,                       FieldName = g.Average(S => S.Price)                   };

// Union Query
//To achieve Select * From Product Where CategoryId =1 union Select *  From Product Where CategoryId = 2 you need to write follofing linq Query

var Result = (from p in db.Product                    where p.CategoryID == 1                    select p).Union(                        from m in db.Product                        where m.CategoryID == 2                        select m                    );