// Specify the data source.

                int[] scores = new int[] { , , ,  };

                // Define the query expression.

                IEnumerable<int> scoreQuery =

                    from score in scores

                    where score >

                    select score;

                // Execute the query.

                foreach(int i in scoreQuery)

                {

                    Console.Write(i + " ");

                }

• Query expressions can be used to query and to transform data from any LINQ-enabled data source. For example, a single query can retrieve data from a SQL database, and produce an XML stream as output.

• Query expressions are easy to master because they use many familiar C# language constructs. For more information, see Getting Started with LINQ in C#.

• The variables in a query expression are all strongly typed, although in many cases you do not have to provide the type explicitly明确地 because the compiler can infer推断 it. For more information, see Type Relationships in LINQ Query Operations (C#).

• A query is not executed until you iterate over the query variable in a foreach statement. For more information, see Introduction to LINQ Queries (C#).

• At compile time, query expressions are converted to Standard Query Operator method calls according to the rules set forth in the C# specification. Any query that can be expressed by using query syntax can also be expressed by using method syntax. However, in most cases query syntax is more readable and concise简洁的. For more information, see C# Language Specification and Standard Query Operators Overview.

• As a rule when you write LINQ queries, we recommend that you use query syntax whenever possible and method syntax whenever necessary. There is no semantic语义的 or performance difference between the two different forms. Query expressions are often more readable than equivalent expressions written in method syntax.

• Some query operations, such as Count or Max, have no equivalent query expression clause子句 and must therefore因此 be expressed as a method call. Method syntax can be combined with query syntax in various ways. For more information, see LINQ Query Syntax versus Method Syntax (C#).

• Query expressions can be compiled to expression trees or to delegates, depending on the type that the query is applied to.IEnumerable<T> queries are compiled to delegates. IQueryable and IQueryable<T> queries are compiled to expression trees. For more information, see Expression Trees (C# and Visual Basic).

The following table lists topics that provide additional information about queries and code examples for common tasks.