SQL query error when trying to reuse calculated field

Hi @Housseiny 

Result is not fully rendered in your query, therefore no value is assigned for ITD_BUD 

You can have 2 option to resolve this. Option one to make calculation in the same query. 

x.budget_base_curr/120 ITD_BUD,
x.actual - (x.budget_base_curr/120) as  "Deviation",

Option 2 is to create a subquery where result is rendered and built your query on top of that

select T.*,

T.actual-T.ITD_BUD as “Deviation”,

IFSAPP.SUB_PROJECT_API.Get_Description(t.PROJECT_ID, t.SUB_PROJECT_ID) Sub_Proj_Des,

IFSAPP.ACTIVITY_API.Get_Description(t.ACTIVITY_SEQ) activity_des,
IFSAPP.Project_Forecast_Item_API.Get_Project_Cost_Element_Desc(t.FORECAST_ID, t.PROJECT_COST_ELEMENT) cost_elm_des

from

(select X.*, x.budget_base_curr/120 ITD_BUD

from

project_forecast_item_all X) T

where 

T.project_id = '20062' and 

T.forecast_version_id = 'M1003'

Hope it is clear