What is LINQ?

We know that a query is a question we pose to the database to retrieve some information that we would like to know. For example, in a database that consists of men and women, you may want to know how many men and how many women. Let us go a step further and say that there are people of all nationalities in the database of men and women. You may want to know how many women who hail from Europe are there. This is only filtering of the information but a query can much more complex. This is of course querying a database, let us say a relational database such as the SQL Server where you use the Structured Query Language(SQL), a special language you have to learn.

All data are not in relational databases and they could be in some kind of an XML document, a web service or something else. For example, in order to find some filtered content in an XML document you would use a language called XQuery which is not the same as SQL. This means there is need to learn another query language.

Beginning with Visual Studio 2008 and .NET Framework 3.5 Microsoft introduced LINQ which stands for Language-Integrated Query an innovation that made it possible to query a SQL Server database, an XML document, Web Services etc with a single lanugage and it is a first class query language.

In Visual Studio you can write LINQ in both VB and C# for any collection that supports IEnumerable or the generic IEnumerable interface (or to put it simply a collection in which one can go through the collection item by item).

For example you may have a list  of names ("John", "Tom", "June", "Diana") etc.  or  the number of rows in a database table , etc. and they can be queried using LINQ.

Need to query SQL Server with LinqPad, review the following posts:

http://hodentekmsss.blogspot.com/2014/12/learn-querying-sql-server-using-linq.html
http://hodentekmsss.blogspot.com/2014/12/learn-querying-sql-server-2012-using.html