Re: SQL Help - Finding Next Lowest Value of Current Row Value

Jeff Adams wrote on 01.10.2011 23:30:
> Greetings,
>
> I have a large table (~19 million records). Records contains a field
> identifying a vessel and a field containing an time (epoch). Using the
> current rows vessel and time values, I need to be able to find the next
> lowest time value for the vessel and use it to compute how much time has
> elapsed between the records. I have tried a scalar subquery in the SELECT,
> which works, but it runs quite slowly. Is there an alternative approach that
> might perform better for this type of query. Any information would be
> greatly appreciated. Thanks...
>
> Jeff

Something like:


SELECT vessel,
        time_column,
        time_column - lag(time_column) over (partition by vessel order by time_column) as diff
FROM your_table

No sure how good that performs though.