TSQL getting the maximum and minimum date for each person and his number

Question

I have a dataset like this:

It is necessary to getting the minimum and maximum date, the person and his number from each frame:

The code sample below: enter link description here

Thanks a lot!

Answer 1

This is an example of a gaps-and-islands problem. I would recommend the difference of row numbers for this:

select person, number_one, count(*) as cnt,
       min(person_date), max(person_date)
from (select t.*,
             row_number() over (partition by person order by person_date) as seqnum,
             row_number() over (partition by person, number_one order by person_date) as seqnum_2
      from t
     ) t
group by person, (seqnum - seqnum_2)

Answer 2

This looks like a gaps-and-islad problem. Here is one way to solve it using window functions:

select 
    min(person_date) person_date_start,
    max(person_date) person_date_end,
    person,
    number_one
from (
    select 
        t.*,
        row_number() over(order by person_date) rn1,
        row_number() over(partition by person, number_one order by person_date) rn2
    from mytable t
) t
group by person, number_one, rn1 - rn2

It is quite unclear what is the logic to generate the id in the outer query. If you want to renumber the records, then you can use row_number():

select 
    row_number() over(order by min(person_date)) id,
    min(person_date) person_date_start,
    max(person_date) person_date_end,
    person,
    number_one