c#中@的3种作用

string strSQL = "SELECT * FROM HumanResources.Employee AS e"
 + " INNER JOIN Person.Contact AS c"
 + " ON e.ContactID = c.ContactID"
 + " ORDER BY c.LastName";

string strSQL = @"SELECT * FROM HumanResources.Employee AS e
 INNER JOIN Person.Contact AS c
 ON e.ContactID = c.ContactID
 ORDER BY c.LastName";

public static void @static(int @int)
 {
   if (@int > 0)
   {
    System.Console.WriteLine("Positive Integer");
   }
   else if (@int == 0)
   {
    System.Console.WriteLine("Zero");
   }
   else
   {
    System.Console.WriteLine("Negative Integer");
   }
}