for what purpose LINQ is use?

ith linq there is compile time syntax check.

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I want add one more point
 and it is very important
when we use general sql sentences or we can say queries they are get executed after submitting to server or database but LINQ provides compilation and execution both in dot net itself.

For me LINQ  is another way of getting things done, the shorter and easy way.
For example. Lets say you  have an array of numbers and you want to get the smallest and the largest number.
You have two choices here. Either use the loop do to this or use a single LINQ statement to return min or max value.

It is a new query language designed by microsoft under .net 3.5 which is used for quering on various object like arrays,collections,sql server database xml files & entities.
                           it is a only replacement of traditional sql which we use for communicating with relational database like oracle, sqlserver ,ms-Access etc.