is there any max() function available in appengine datastore to find max of selected records

[pyrocks]

HI good morning,

i am very new to the appengine.
anybody help me In finding the maximum salary from the employee table
in appengine datastore.

here shall we have any max() function available like in oracle to find
max salaried employee.

Thanks and regards.

[Greg]

On Mar 14, 3:48 am, pyrocks <kiranbe...@gmail.com> wrote:
> here shall we have any max() function available like in oracle to find
> max salaried employee.

In a word, no. You need to store the maximum salary in the datastore,
and every time time a salary changes check to see if it exceeds the
maximum, and update it if so.

[Takashi Matsuo]

Hi,

Perhaps you can order by salary property descending, and just get the
first one, for getting max value.

max_salaried_employee = Employee.all().order("-salary").get()
max_salary = max_salaried_employee.salary

hope this helps

--
Takashi Matsuo
Kay's daddy

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[Eli Jones]

Like Takashi says.. you can effectively get the max() for a numeric property (db.FloatProperty() or db.IntegerProperty()) by issuing a command like he gave.. or a more SQL looking query like this:

result = db.GqlQuery("Select * from Employee Order By salary desc").fetch(1)

maxsalary = result[0].salary

Other built in SQL functions like Sum() aren't really doable though. (Not in a simple way).

[Max]

Order by salary means an extra index will be built over this field,
which will affect your write speed.

Use a global variable to store max(salary)

On Mar 15, 10:12 am, Takashi Matsuo <matsuo.taka...@gmail.com> wrote:
> Hi,
>
> Perhaps you can order by salary property descending, and just get the
> first one, for getting max value.
>
> max_salaried_employee = Employee.all().order("-salary").get()
> max_salary = max_salaried_employee.salary
>
> hope this helps
>
> --
> Takashi Matsuo
> Kay's daddy
>

[Ulrich]

Max wrote:
> Order by salary means an extra index will be built over this field,
> which will affect your write speed.
>
> Use a global variable to store max(salary)
>

If you store this global variable in the datastore and have a high
number of inserts, you have to update this global variable too often and
it will not work without some kind of sharding.

-Ulrich

[Jeff Schnitzer]

On Tue, Mar 16, 2010 at 12:01 PM, Ulrich <miere...@googlemail.com> wrote:
> Max wrote:
>>
>> Use a global variable to store max(salary)
>
> If you store this global variable in the datastore and have a high number of
> inserts, you have to update this global variable too often and it will not
> work without some kind of sharding.

Even if there are zillions of salaries and they are constantly
changing, it's still unlikely that max(salary) is going to change
often enough for this to be a problem.

Jeff