SQL partition by on date range

Question

Assume this is my table:

ID  NUMBER  DATE
------------------------
1   45      2018-01-01
2   45      2018-01-02
2   45      2018-01-27

I need to separate using partition by and row_number where the difference between one date and another is greater than 5 days. Something like this would be the result of the above example:

ROWNUMBER   ID  NUMBER  DATE
-----------------------------
1           1   45      2018-01-01
2           2   45      2018-01-02
1           3   45      2018-01-27

My actual query is something like this:

SELECT ROW_NUMBER() OVER(PARTITION BY NUMBER ODER BY ID DESC) AS ROWNUMBER, ...

But as you can notice, it doesn't work for the dates. How can I achieve that?

Answer 1

You can use lag function :

select *, row_number() over (partition by number, grp order by id) as [ROWNUMBER]
from (select *, (case when datediff(day, lag(date,1,date) over (partition by number order by id), date) <= 1 
                      then 1 else 2 
                 end) as grp
      from table
     ) t;