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Abstraction: Abstraction lets you focus on what the object does instead of how it does it That means we use the object without knowing the source code of the class. Encapsulation: Encapsulation means hiding the internal details or mechanics of how an object does something. Encapsulation is wraping data into single unit.

A struct is a value type, while a class is a reference type. When we instantiate a class, memory will be allocated on the heap. When struct gets initiated, it gets memory on the stack. Classes can have explicit parameter less constructors. But structs cannot have this. Classes support inheritance. But there is no inheritance for structs. A struct cannot inherit from another struct or class, and it cannot be the base of a class. Like classes, structures can implement interfaces. We can assign null variable to class. But we cannot assign null to a struct variable, since structs are value type. We can declare a destructor in class but can not in struct.

select Count(ID), Name, Email,Comment FROM TableName      group by Name, Email,Comment having Count(ID)>1