automatic surface calculation

[bolognesiedalla]

Hello everybody. I am creating an app for interventions in the countryside. In each intervention I have the choice of land as an enumlist, to choose more land. In the same table (named "CAMPAGNA") I would like to automatically fill the column [SUP. TRATTATA (ha)], which represents the sum of the areas of the land chosen for the intervention that is being completed. The values of the areas are in a second table called "TERRENI". Is it possible to calculate it with an expression?

[Marc_Dillon · Accepted solution]

https://help.appsheet.com/en/articles/2357307-sum

https://help.appsheet.com/en/articles/4575708-list-dereference

[bolognesiedalla]

Thanks ... I have read the articles and they are very helpful. My difficulty is in constructing the expression that from  CAMPAGNA[APPEZZAMENTO] enumlist, compares the ID_TERRENO of the enumlist with the ID_TERRENO of the LANDS table, takes the corresponding surface. then Sum the values.
I did tests, but I did not reach a satisfactory result. 

Could you help me with the various steps?

[Steve]

What have you tried?

[bolognesiedalla]

I was not familiar with the expression IN (). I completed the formula like this:

SUM(
SELECT(
TERRENI[SUP. (ha)],
IN([ID_TERRENO],[_THISROW].[APPEZZAMENTO] )
)
)