Finding continuous ranges in a set of numbers

Question

I have a reasonably large set of phone numbers (approximately 2 million) in a database table. These numbers have been inserted in blocks, so there are many continuous ranges

Answer 1

SQL can't really do this in a single query (except there are native SQL enhancements I don't know about), because SQL can't access the row 'before' or 'after'.

You need to go through the sequence in a loop.

You may try NHibernates Enumerable, which doesn't load the entities into memory, but only creates proxies of them. Actually I don't think that it is a good idea, because it will create proxies for the whole 2 million numbers.

Plan B, use paging. Roughly, it looks like this:

List result = new List();

int input = 1012;
int pageSize = 100;
int currentPage = 0;
int expectedNumber = input;

bool carryOn = true;

while(carryOn)
{
  var numbers = session
    .CreateQuery("from PhoneNumber pn where pn.Number > :input")
    .SetInt("input", input)
    .SetFirstResult(currentPage * pageSize)
    .SetMaxResult(pageSize)
    .List();

  foreach(var number in numbers)
  {
    expectNumber++;
    if (number.Number != expectedNumber) 
    {
      carryOn = false;
      break;
    }
    result.Add(number);
  }

  currentPage++;
}

And the same for the range before in the other direction.