LINQ to SQL Queries
You define LINQ to SQL queries by using the same syntax as you would in LINQ. The only difference is that the objects referenced in your queries are mapped to elements in a database. For more information, see Introduction to LINQ Queries (C#).
LINQ to SQL translates the queries you write into equivalent SQL queries and sends them to the server for processing. More specifically, your application uses the LINQ to SQL API to request query execution. The LINQ to SQL provider then transforms the query into SQL text and delegates execution to the ADO provider. The ADO provider returns query results as a DataReader. The LINQ to SQL provider translates the ADO results to an IQueryable collection of user objects.
The following illustration depicts this general flow.
Most methods and operators on .NET Framework built-in types have direct translations to SQL. Those that LINQ cannot translate generate run-time exceptions. For more information, see SQL-CLR Type Mapping (LINQ to SQL).
The following table shows the similarities and differences between LINQ and LINQ to SQL query items.
LINQ to SQL Query
Return type of the local variable that holds the query (for queries that return sequences)
Specifying the data source
Uses the From (Visual Basic) or from (C#) clause
Uses the Where/where clause
Uses the Group…By/groupby clause
Uses the Select/select clause
Deferred versus immediate execution
Uses the Join/join clause
Remote versus local execution
For more information, see Remote vs. Local Query Execution (LINQ to SQL).
Streaming versus cached querying
Not applicable in a local memory scenario