LINQ Max

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Bill McCormick

How would you structure a Linq statement using Max to return the record with
the greatest (newest) datetime field?
 
Bill McCormick wrote on 29-6-2009 :
How would you structure a Linq statement using Max to return the record with
the greatest (newest) datetime field?
Click to expand...

Why not sort it (descending, so that the newest date is on top) and
then take the first?

Hans Kesting
 
How would you structure a Linq statement using Max to return the
record with the greatest (newest) datetime field?
Click to expand...

Try:
http://msdn.microsoft.com/en-us/vbasic/bb737922.aspx

They are in VB, but it is fairly straighforward to convert, as boht use
extension methods.

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Bill McCormick wrote on 29-6-2009 :

Why not sort it (descending, so that the newest date is on top) and then
take the first?
Click to expand...
Because I like to be fancy :) That, and I'd like to learn how these things work.

Thanks.
 
Try:
http://msdn.microsoft.com/en-us/vbasic/bb737922.aspx

They are in VB, but it is fairly straighforward to convert, as boht use
extension methods.
Click to expand...

Thanks. I just found the exact same page before I saw your post and it was
helpful. Here's what I did:

var ctare = (from t in TTares
where (t.TTareDateTime) == (from r in TTares
select r.TTareDateTime).Max()
select t.TTareWeight).Single<double>();

I don't like that it's making the comparison though. I think there must be a
more succinct method.

Thanks.
 
Bill said:
Thanks. I just found the exact same page before I saw your post and it
was helpful. Here's what I did:

var ctare = (from t in TTares
where (t.TTareDateTime) == (from r in TTares
select r.TTareDateTime).Max()
select t.TTareWeight).Single<double>();
Click to expand...

It might be more efficient to compute the maximum only once outside of
the where predicate e.g.
DateTime latest = (from r in TTares select r.TTareDateTime).Max();

var ctare = (from t in TTares
where t.TTareDateTime == latest
select t.TTareWeight).Single<double>();
 
It might be more efficient to compute the maximum only once outside of
the where predicate e.g.
DateTime latest = (from r in TTares select r.TTareDateTime).Max();

var ctare = (from t in TTares
where t.TTareDateTime == latest
select t.TTareWeight).Single<double>();
Click to expand...

OK. Thanks, I like that. But still, there must be some other way to do this
with having to compare the DateTime field. If not not, maybe I use the
previously suggested Top 1 method.

Bill
 
Because I like to be fancy :) That, and I'd like to learn how these
things work.
Click to expand...
Have learned that the other alteratives aren't as good, I've come around to
your suggestion:

var ctare = (from t in TTares
orderby t.TTareDateTime descending
select t.TTareWeight).First();

Thanks,

Bill
 
Strange, if I compare the two syntaxes, the TOP 1 is about twice slower than
the subquery. With the batch (show execution plan):

SELECT TOP 1 * FROM ParamsProjetDefauts ORDER BY TimeStampRef DESC;
SELECT * FROM ParamsProjetDefauts WHERE TimeStampRef = (SELECT
MAX(TimeStampRef) FROM ParamsProjetDefauts);


the first query, accordingly to the query execution plan, take 68% of the
time to run the whole batch (while the subquery takes only 32 % of the batch
time). The solution you adopted is (probably) translated to the TOP 1, case.



Vanderghast, Access MVP
 
Strange, if I compare the two syntaxes, the TOP 1 is about twice slower
than the subquery. With the batch (show execution plan):

SELECT TOP 1 * FROM ParamsProjetDefauts ORDER BY TimeStampRef DESC;
SELECT * FROM ParamsProjetDefauts WHERE TimeStampRef = (SELECT
MAX(TimeStampRef) FROM ParamsProjetDefauts);


the first query, accordingly to the query execution plan, take 68% of
the time to run the whole batch (while the subquery takes only 32 % of
the batch time). The solution you adopted is (probably) translated to
the TOP 1, case.
Click to expand...

Agreed, the TOP 1 translates. And the tining results are surprising. I'll do
some testing here to try to duplicate your results.

Thanks.
 
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