Question

I have a table in SQL Server where, for each row r at time t, I would like to find the first t + i for some function of r where abs(f(r, t + i) - f(r, t)) > epsilon.

I can imagine doing this with two cursors, but this seems highly inefficient.

Any of the T-SQL gurus out there have any advice?

Answer 1

select a.t, b.t  --- and what other columns you need
from tbl a -- implicitly each row of table
cross apply (
    select top(1) * -- the first, going upwards along b.t
    from tbl b
    where a.t < b.t -- look for records with later t than the source row
      and <here's your function between a row and b row>
    order by b.t asc
) x