Expression SUM with concatenation

[#1]

hello,

I have a problem with my expression.

I try to do a sum, with a concatenation of 2 fields.

[civile_Year/month] = 01.2011, 02.2011, 03.2011, 04.2011 ....

[Num_month] = 01, 02, 03, 04, 05, 06, 07, 08, 09, 10, 11, 12

[civile_year] = 2008, 2009, 2010, 2011

I want to display the volume for the max date that the user have selected.

for example : if he select [civile_year] = 2011 and [Num_month] from 01 to 10, I want to display the volume for [civile_Year/month] = 10.2011

My expression :

=sum( {<[civile_Year/month]= {$(=MaxString([Num_month]))&'.'&[civile_year]}>} Volume)

I have try lots of synthaxe like :

=sum( {<[civile_Year/month]= {(concat($(=maxstring([Num_month]))&$(=max([civile_year])),'.')}> } Volume)

Someone can help me ?

Thanks in advance.

[#2]

Previous year last month must be display when a year and a month are selected.

example : if january 2011 is selected, the data displayed are 1 column with january 2011 and one with january 2010

[#3]

In script :

load

left(([civile_Year/month]),4)  as Year,

left(([civile_Year/month]),4) & right(([civile_Year/month]),2) as YearMonth

from ......

jan 2011 :

=sum({Year ={$(=max(Year))},YearMonth={$(=max(YearMonth))}}Volume)

jan 2010 :

=sum({Year ={$(=max(Year)-1)},YearMonth={$(=max(YearMonth))}}Volume)

Regards,

Antony.

[#4]

it works, thanks you