Linq is short for Language Integrated Query. If you are used to using SQL to query databases, you are going to have something of a head start with Linq, since they have many ideas in common. Before we dig into Linq itself, let’s step back and look at what makes SQL different from C#.

Imagine we have a list of orders. For this example, we will imagine they are stored in memory, but they could be in a file on disk too. We want to get a list of the costs of all orders that were placed by the customer identified by the number 84. If we set about implementing this in C# before version 3 and a range of other popular languages, we would probably write something like (assuming C# syntax for familiarity):

List Found = new List();

foreach (Order o in Orders)

if (o.CustomerID == 84)

Found.Add(o.Cost);

Here Im describing how to achieve the result we want by breaking the task into a series of instructions. This approach, which is very familiar to us, is called imperative programming. It relies on us to pick a good algorithm and not make any mistakes in the implementation of it; for more complex tasks, the algorithm is more complex and our chances of implementing it correctly decrease.