With built-in LINQ extension methods, and lambda expressions, Visual Studio 2008 allows us to write SQL-like statements in C# when invoking these methods. The syntax of these statements is called LINQ query syntax, and the expression in query syntax is called a query expression.

For example, we can change this statement:

var veges6 = products.Where(p => p.ProductName.Contains("vegetable"));

To the following query statement, by using the new LINQ query syntax:

var veges7 = from p in products
where p.ProductName.Contains("vegetable")
select p;

In the above C# statement, we can directly use the SQL keywords select, from, and where to "query" an in-memory collection list. In addition to the in-memory collection lists, we can use the same syntax to manipulate data in XML files, in the dataset, and in the database. In the following sections, we will see how to query a database using LINQ to SQL.

Combined with the anonymous data type, we can shape the result of the query in the following statement:

var candyOrVeges = from p in products
where p.ProductName.Contains("candy")
|| p.ProductName.Contains("vegetable")
orderby p.UnitPrice descending, p.ProductID
select new { p.ProductName, p.UnitPrice };

As you have seen, query syntax is a very convenient, declarative shorthand for expressing queries using the standard LINQ query operators. It offers a syntax that increases the readability and clarity of expressing queries in code, and can be easy to read and write correctly.

Not only is query syntax easy to read and write, Visual Studio actually provides complete intellisense and compile-time checking support for query syntax. For example, when typing in p and the following dot, we get all of the Product members listed in the intellisense list, as shown in the following image:

If there is a typo in the syntax (as is the case in this statement: where p.productName.Contains("vegetable")), the compiler will tell you exactly where the mistake is is and why it is wrong. There won't be any run-time error such as "invalid SQL statement". The following image shows the error message when there is a typo in the syntax:

As you can see, you can write a LINQ statement in the query syntax, much like when you are working with a database in Query Analyzer. However, the .NET common language runtime (CLR) has no notion itself of the query syntax. Therefore, at compile time, query expressions are translated to something that the CLR does understand: method calls. Under the covers, the compiler takes the query syntax expressions and translates them into explicit method invocation code that utilizes the new LINQ Extension Method and lambda expression language features in C# 3.0.

For example, the candyOrVeges query expression will be translated to this method invocation call:

products.Where(p => p.ProductName.Contains("candy") || p.ProductName.Contains("vegetable")).OrderByDescending(p => p.UnitPrice).ThenBy(p=>p.ProductID).Select(p=>new { p.ProductName, p.UnitPrice })

In general, query syntax is recommended over method syntax because it is usually simpler, and more readable. However, there is no semantic difference between method syntax and query syntax.