is it possible to declare variable at runtime, name of variable are stored in database. we have it declare it and initialise it at runtime.. how ???????????

This is useful when the methods/variables of an instance are based on a data file that isn't available until runtime.

Yes, you can.

Is it a requirement to use the name of the variable stored in database?

In order to mantain the name of the variable at run time, I would suggest to use a list of type Dictionary having the name of the variable as the key, and the variable it self as value.
In order to be a homogenius dictionary, I would suggest to cast all the variables to Object if not all of them are of the same type (ie: string)

Example:

Dictionary<string, string> MyListOfVariables;
//
foreach(string newVariableName in DataBaseListOfVariablesNames)
{
    string n = "";
    MyListOfVariables.Add(newVariableName, n));
}

Hope this helps.