Question

I have a table dbo.counters with columns idx, idx_device, DateTime, Data1, Data2 etc.

• idx is key and autoincremental
• idx_device refers to another table, hundreds of rows may exists in table with same idx_device value
• DateTime is TimeStamp when record has been written

I need to have from each idx_device one complete row which is closest to a specific DateTime, but not higher than.

I got already following formula, but this does not output all columns from table:

select max(DateTime), idx_device from dbo.counters 
    WHERE DateTime <= '02/04/12 23:59:59.995' 
    group by idx_device

guess should be something small, but I hang… thanks

Answer 1

Here is a solution using Common Table Expressions:

with cte as
    (select 
        *, 
        row_number() 
        over (partition by idx_device order by DateTime desc) as rowno
    from dbo.Counters
    where DateTime < '2012-02-04')
select * from cte where rowno = 1