Re: HELP! SQL Question

John N. Zeigler wrote:
>
> We have a very large database with historical information. When we
> update information, we add a new row and keep the old info. We do this
> by using a real number column that is similar to a date field. That is,
> the larger the number, the more recent the data. So, to extract the most
> recent information, I want to select the rows with the highest real
> numbers. For example, if I have 3 rows with information on parameter A
> I want to extract the one row with the largest real number. I may have
> 5 rows for parameter B, 12 rows for parameter C, etc. For each of these
> parameters, I want only the row with the highest real number. For my
> output, I want one row returned for each parameter and this row must
> contain the largest value in the real number column for that parameter.
> Example of output:
>
> Parameter Real_number
>
> A 5.3
> B 3.1
> C 6.2
> D 1.4
> E 9.2

In order to achieve the above output you only need the following: SELECT parameter, MAX(real_number)
FROM your_table
GROUP BY parameter

With a large table this may not be very fast, and you may want to think about other ways to structure the data -- e.g., flagging the most recent row or moving history to another table.

Beth Received on Thu Feb 22 1996 - 00:00:00 CET