Merging data in a single SQL table without a Cursor

Question

I have a table with an ID column and another column with a number. One ID can have multiple numbers. For example

ID | Number
 1 |  25
 1 |  26
 1 |  30
 1 |  24
         


        

Answer 1

The key observation is that a sequence of numbers minus another sequence is a constant. We can generate another sequence using row_number. This identifies all the groups:

select id, MIN(number) as low, MAX(number) as high
from (select t.*,
             (number - ROW_NUMBER() over (partition by id order by number) ) as groupnum
      from t
     ) t
group by id, groupnum

The rest is just aggregation.