sum expressión

[jtrillori]

Morning

i have the next expression:

(-(sum( {$<[FD_F_CUENTA_MAYOR] = {'70500002'},FD_F_FECHA_CONTABILIZACION={"=FD_F_FECHA_CONTABILIZACION=fechas"}>} FD_F_IMPORTE)))

where fechas as a variable and works ok.

but now i need get the previous year information.

we have two fields (año and mes), when the year (año) 2013 and the month(mes) (2013 -feb) are selected, i have two variables that take a diferents values:

fechas ( 28/02/2013) and fechas_prev_year (29/02/2012)

i try to modify the expression including the variable fechas_prev_year but it doesn´t work.

(-(sum( {$<[FD_F_CUENTA_MAYOR] = {'70500002'},FD_F_FECHA_CONTABILIZACION={"=FD_F_FECHA_CONTABILIZACION=fechas_prev_year"}>} FD_F_IMPORTE)))

i think that the problem is a año and mes selection because the range is for other year and other month, but i don´t know how can i solve it,

i´m very pleassed with your help.

regards

and sorry for my english