Count consecutive duplicate values in SQL

Question

I have a table like so

ID     OrdID     Value
1      1          0     
2      2          0
3      1          1
4      2          1
5      1          1
6      2          0
7      1          0
8      2          0
9      2          1
10     1          0
11     2          0

I want to get the count of consecutive value where the value is 0. Using the example above the result will be 3 (Rows 6, 7 and 8). I am using sql server 2008 r2.

Answer 1

I am going to presume that id is unique and increasing. You can get counts of consecutive values by using the different of row numbers. The following counts all sequences:

select grp, value, min(id), max(id), count(*) as cnt
from (select t.*,
             (row_number() over (order by id) - row_number() over (partition by value order by id)
             ) as grp
      from table t
     ) t
group by grp, value;

If you want the longest sequence of 0s:

select top 1 grp, value, min(id), max(id), count(*) as cnt
from (select t.*,
             (row_number() over (order by id) - row_number() over (partition by value order by id)
             ) as grp
      from table t
     ) t
group by grp, value
having value = 0
order by count(*) desc