Question

select top 1 ROW_NUMBER() OVER (ORDER BY eventtime desc) as id,
Eventcode, eventtime as et, status from cfw.dbo.DCTBLEVENTINFO 
where MeterID = 4722 and EventTime between convert(date,'2011-10-21') 
and dateadd(day,1,convert(date,'2011-10-26')) 
and EventCode = 13

Original resultset:

id  Eventcode   et                    status
1   13        2011-10-26 15:00:00.000   1

The above query returns the perfect result set, but if I use the same query like the following manner it returns the wrong result

SELECT temp.et 
  FROM (SELECT TOP 1 ROW_NUMBER() OVER (ORDER BY eventtime desc) as id,
               Eventcode, 
               eventtime as et, 
               status 
          FROM cfw.dbo.DCTBLEVENTINFO 
         WHERE MeterID = 4722 
           AND EventTime BETWEEN CONVERT(date,'2011-10-21') 
                             AND DATEADD(day,1,convert(date,'2011-10-26')) 
           AND EventCode = 13) temp 
 WHERE status = 1

Result set for the above query :

et
------------------------
2011-10-21 21:42:00.000

It returns some other date. I can’t find the problem.

Answer 1

Try adding an ORDER BY to your sub select.

Something like

select  temp.et 
from    (
            select  top 1 
                    ROW_NUMBER() OVER (ORDER BY eventtime desc) as id, 
                    Eventcode, 
                    eventtime as et, 
                    status 
            from    cfw.dbo.DCTBLEVENTINFO  
            where   MeterID = 4722 
            and     EventTime between convert(date,'2011-10-21') and dateadd(day,1,convert(date,'2011-10-26'))  
            and     EventCode = 13
            ORDER BY eventtime desc
        )   temp 
where   status=1

Please always remember Without ORDER BY, there is no default sort order.

Furthermore, remeber the Logical Query Processing Phases – Order of Statement Execution

1. FROM
2. ON
3. OUTER
4. WHERE
5. GROUP BY
6. CUBE | ROLLUP
7. HAVING
8. SELECT
9. DISTINCT
10. ORDER BY
11. TOP