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

Theoretically the items in a set have no particular value, so I'm assuming you also have some continuous ID column that defines the order of the numbers. Something like this:

ID  Number
1   1000
2   1001
3   1002
4   1010
5   1011
6   1012
7   1013
8   1020
9   1021
10  1022

You could create an extra column that contains the result of Number - ID:

ID  Number  Diff
1   1000    999
2   1001    999
3   1002    999
4   1010    1006
5   1011    1006
6   1012    1006
7   1013    1006
8   1020    1012
9   1021    1012
10  1022    1012

Numbers in the same range will have the same result in the Diff column.