Hi Dave
Yes, 100% the best solution .... I did the same thing a while back, I just have a separate copy of the data in a "latest" table and the Java code just runs a second SQL statement to update it when writing a new record (I've never been a trigger fan).
I found myself looking at the "find the latest" query again though in the process of building a "demo mode" into our application, which will replay a finite set of data on a rolling loop by moving it forward in time, and also has to simulate the continuous updating of the "latest" table so the the business logic will be appropriately fooled.
My next tweak will be to cache the "latest" table in the Java layer ;-)
Cheers
Dave
On Fri, Feb 25, 2011 at 10:50 AM, Dave Johansen
<davejohansen@gmail.com> wrote:
On Thu, Feb 24, 2011 at 4:38 PM, Dave Crooke
<dcrooke@gmail.com> wrote:
Thanks to all .... I had a tickling feeling at the back of my mind that there was a neater answer here. For the record, times (all from in-memory cached data, averaged over a bunch of runs):
Dependent subquery = 117.9 seconds
Join to temp table = 2.7 sec
DISTINCT ON = 2.7 sec
So the DISTINCT ON may not be quicker, but it sure is tidier.
Cheers
Dave
I also added a 4th version that uses a permanent table that's auto-populated by a trigger with the rid of the most recent entry from the main table, so it's a simple join to get the latest entries.
Dependent subquery = (killed it after it ran for over 10 minutes)
Join on temp table = 1.5 seconds
DISTINCT ON = 2.9 seconds
Join on auto-populated table = 0.8 seconds
Dave
