LINQ looks like another amazingly simple move for app developers (I've written a few DB apps myself over the years).  While Microsoft provides support for Objects, SQL and XML, others provide for other platforms such as Oracle, MySQL and PostgreSQL (http://code2code.net/DB_Linq/).  The reason why it is so nice is because the gap between the process of writing SQL queries and then programming them into your code is considerably removed.  For example, a query might now look like:

var q = from p in db.Products            
         where p.ProductName == "Pen"
         select p.ProductID;        

I think that looks very much like a SQL query, which is really good for developers and database peeps alike, especially since the underlying execution is very efficient. To make understanding all this easier there has been a number of articles written including...

Beginning LINQ development, Part 1

Brian Eastwood, Site Editor

The Language Integrated Query, or LINQ, is one of the most important of the new features afoot in VB 9.0 and C# 3.0.Developers can use LINQ to query to data sources like ADO.NET, SQL and XML. The idea, of course, is that data queries are now an integrated part of Visual Basic and C# and an immeasurable improvement over data integration in the days of preprocessors.

LINQ first emerged at PDC 2005, and though it is intended for the next version of Visual Studio, code-named "Orcas," LINQ is available for use with Visual Studio 2005.

A good starting point for learning more about LINQ is Hooked on LINQ, a wiki for anyone interested in dipping his toe in the water. Among the site's resources are "five-minute overviews" of using LINQ with objects, SQL and XML.

For more on LINQ-to-SQL queries, which were previously called DLINQ queries, check out the Scott Guthrie post Understanding LINQ to SQL Query Translations. (Guthrie is the head of ASP.NET development at Microsoft.) Here you can find hints for working with stored procedures, Where clauses and mathematics functions.

Beginning LINQ development, Part 1

and

Beginning LINQ development, Part 2
LINQ, the Language Integrated Query, dramatically changes database programming in Visual Studio 2008. Here we examine the ins and outs of LINQ to SQL queries.

Beginning LINQ development, Part 3
LINQ works well for managed code and for RAD, but the language enhancements it brings to the .NET Framework should be considered carefully.

Visual Studio 2008 Learning Guide: LINQ
This section of the Visual Studio 2008 Learning Guide looks at LINQ, which is arguably the most important new feature of VS 2008.

ttfn

David